Disclaimer: This started as a brief reply to post a cool video and turned into a thesis on what I consider to be the best way to approach language learning, based on academic knowledge and a few years of failing miserably at it (If you plan on reading my post you might want to get a drink first - hopefully you’ll find the content worth it 
).
I’m currently studying Cognitive Neuropsychology (the main reason I struggle with Japanese - time interference) and have qualifications in language learning and teaching (including TESOL).
That video EigaKantoku linked is gold, seriously.
From a neurological viewpoint, the following video supports their ideas:
So when we learn by taking classes and memorizing rules and vocabulary lists, we are largely utilizing the neocortex. We are trying to form conscious, explicit connections in our minds to learn a language, but that’s almost impossible to do, due to the haphazard way that languages develop. If languages were designed to be perfectly logical using computer algorithms designed to make it simple and efficient, it would actually work quite well, but that’s just not how language currently works. It’s sloppy as hell, full of exceptions, and just pure contradictions and bad logic.
Fortunately we don’t need it to be that logical and efficient to “get it” because our brains are almost obsessed with detecting and figuring out patterns. And as long as the conscious mind is even remotely directed towards sources of patterns, the implicit or subconscious parts of our brains will start to take over. One of the biggest contributions our conscious or explicit mind makes, is actually deciding that we want to pursue said pattern and direct our behaviors towards them (though even this is often driven by implicit processes).
We’ve long known that the implicit mind is far more powerful than the explicit. Though Freud made some shockingly bad inferences about what was within our implicit mind and how to manipulate it, he at least opened up the investigations into it, which was essentially the foundations of all psychology (luckily it got massively better than the crap Freud was peddling).
As the video mentioned, learning to ride a bicycle is part of implicit memory, and as the saying goes “It’s like riding a bike,” it’s not something you ever forget. If you haven’t done it for awhile, you might be a bit rusty at first, but then you’re right back on par even 20-30 years later. This is why when patients have amnesia, they can completely forget their childhood and learning how to read and write and use language, but they can still do it. You don’t need to consciously remember the rules, they will become “hardwired” into your system. It’s the same with amnesiac musicians. They may not be able to tell you the names of notes or any music theory. They may even tell you that they can’t play, but you hand them their instrument and there is no degradation of skill whatsoever.
So with a language, it’s not important to explicitly remember things, you just have to do it enough, over and over and over until it is hardwired in. But this process needs to happen with the actual language, not with bits and pieces of it. The main benefit of the explicit processes is to identify rare things in the language that you are not likely to be exposed to enough in order for it to become implicit automatically through exposure. Just like in English, you are likely to be ignorant of tons of words that are specific to a field like engineering or medicine, so there is benefit to explicitly learning these terms. However, if you get into those fields, you don’t need to maintain a list of those new words to make sure you don’t forget them, because you are using them now so often that they will be hardwired in and you won’t need to explicitly or actively try to remember them.
Introductory courses in a language are still extremely beneficial as they prime the brain and allow it to have a starting platform to build on. You definitely could do it through pure immersion, but it will be much more painful and a bit less efficient. Our explicit processes are helpful in evaluating our problems and then determining the best way to overcome them. So if you are consistently misunderstanding or not getting something, i,e, it’s not happening naturally, making the conscious decision that you need to look it up and figure out why things aren’t connecting, which may then require some artificial repetition (e.g. Anki) to get it hardwired.
Your brain is also immensely better at learning something when it needs to know that thing, in order to do something right now, than it is at learning something that it might need, in order to do something later.
So go through your basic grammar activities and just make sure you understand the concepts, rather than memorize the concepts. Understanding is the key, not memorization. Once you’re done with a basic course (book, class, etc) start consuming content that is also basic.
Don’t focus on understanding everything, focus on trying to understand anything. Don’t be discouraged about what you don’t know, but rather be massively (MASSIVELY) impressed by what you do understand. This is incredibly important as you need to give your brain positive feedback to be motivated to continue. Your brain will naturally be inclined to reject anything that is consistently paired with negative evaluations and emotions. Your explicit mind may find something silly, but your implicit mind is like a child and doesn’t care an ounce about social conventions or what’s “cool.” So even if you pretend to be excited and way overplay it, your implicit mind will hardly know the difference. That said, you actually should be super excited with any and all progress, as if you typically pick anyone around you at random (in an English dominated country), and show them a page of Japanese, they likely can’t understand anything in it at all, or even decipher a single character to produce a sound (or even know it’s Japanese that they are looking at)
I suggest you consume the material without any English translations at all. Allow it to frustrate your brain that it doesn’t understand what it’s experiencing, without allowing yourself as a whole to be frustrated with the experience (this is a bit difficult to do and thus takes determination). Try to spend the vast majority of your study with brand new content, or at least content you haven’t seen for over a week or so, but the newer the better.
Consume as many different things as you can, as much as you can. Your brain will start to flag things that you are seeing a lot, but don’t understand. When you notice it, without trying too hard to notice, look it up so you can figure it out and your brain will be completely primed to remember it, with little effort.
Then occasionally, once every few months or so, go back to your basic grammar book and read through it quickly. You will find that the things that weren’t hardwired yet, will suddenly stick out, and you will start to notice that thing all over the place in the content you are consuming, as it also becomes hardwired.
When you get to the point that there’s little in your basic grammar book that you don’t have hardwired, do a new course that’s a bit more advanced. If you consumed a crazy amount of content like you were supposed to, you will likely find that a lot of it you will already know to some degree, but the explicit instructions may help sort out small misunderstandings you had, which will naturally stick in your head, as you have something real to apply it to. The things you don’t know, will also stand out more and your brain will try to absorb it like a sponge so it can figure out the rest of the patterns you have been constantly exposing it to.
So it is necessary to be constantly exposed to material that is unintelligible to you in order to trigger this reaction. This then allows you to view things that you can’t understand, as not frustrating, but rather priming you for future comprehension. Just make sure when you consume this content, you actively pay attention to what you don’t know. Absorb it, don’t skim over it.
On the side, you can do a few things to speed up this process.
Choose something you are highly motivated to understand in Japanese, and once a week or so, read or listen to it again. Do not look at the English translation at all. Choose a part of it that takes no more than 30-60 mins to consume. You should find that each time you do this, you understand it a little more or pick up on patterns that you are also noticing in your other content. Still don’t look up the translations for this. Instead, when you are consuming other material, if you happen to come across the same thing, look it up for that material. To your brain, it will feel like you have discovered secret treasure. It will be fun and interesting and you’re brain will be very unlikely to lose that info once discovered.
When you get to the point that you understand nearly everything in your chosen motivating content, look up the rest of it. When you think you can read/listen to everything and understand it, that’s when you should look at the translations and see how they align with your understanding. If they don’t match, look it up and see why. You may find that occasionally your understanding is better than the translation (depending on their quality). Then simply rinse and repeat with a new motivating content, or perhaps more of the same one (a new chapter or episode).
I would also suggest getting an SRS program like Anki and downloading either a 1000 word or 1000 sentence deck that contains the most commonly used words with basic sentence structures. However, I don’t suggest you use it as intended, for the most part. Make sure they have the proper English translations and are well written (read as not auto-generated), preferably with native audio. Make sure you choose the option where all the cards are unlocked at once. Then spend at most 10-15 mins a day zooming through them as fast as you can, but not so fast that you can’t absorb them a bit. Don’t try too hard to translate or to remember the translations. When you read/hear the Japanese, see if the meaning immediately comes to you. If it doesn’t, read the translation once or twice tops (just enough to absorb what you are reading), choose the Very Hard option (or whichever option will make it pop back up the next day or at the very end of the deck) and move on to the next one. If you immediately know the meaning, choose the Very Easy option so it doesn’t show up again as long as possible. Never choose a middle option. You either know it completely and automatically or you don’t. The key here is to get through each card as quickly as possible while still comprehending what you are exposed to.
A few things will be at work here neurologically. The speed will help convince your brain that it needs to do this stuff quickly. The speed will also allow you to get through a lot more content in a shorter time. Failing each one that you don’t completely and immediately know will disallow your mind from being happy with partial success and drive it to absorb the content quicker. You are also getting a lot of repetition and exposure in this way, as you are constantly re-exposed to the ones you are failing. But the true purpose is not to learn these things through the cards themselves, but to prime the brain to recognize them when you see them in native content. That’s when they will truly hard-wire in. If you come across something weird in native content you are having trouble with, you can pop an example of it into your deck, just make sure not to do it too often or waste too much time making cards (that has completely destroyed my learning three different times).
If you get to the stage where you are zooming through the cards and it seems pointless, you’re right, it is. Get a new deck or just stop using them. It could be beneficial though to use new decks that are weird content specific, that is, content you would like to consume that isn’t common. For instance get a deck with fantasy terms as you tackle trying to read Harry Potter.
At some point, you will understand more of the language than you don’t, and you can choose to explicitly learn things that you know you are having trouble with or are niche subjects that you need to actively learn about. At that point, it will be so much easier to learn as you have a strong base in the language and your brain will be motivated to absorb it, as it loves to finish the puzzle. You will also be able to learn the things you don’t know from native material, which is almost always better than learning it from something that’s been translated and taught from the perspective of a foreign language.
Now I just wish I had the time to follow my own advice
As a post note, I think I can say with some evidence that I am a master at learning explicitly. I’ve attended university twice now (triple majoring the first time) and have maintained a nearly perfect GPA each time. I also believe this is exactly why I’ve failed to learn Japanese in the past. It just doesn’t work the same way as it does with learning other things. I believe this has sabotaged my efforts in the past, as I was trying to use the same processes I always do, and kept feeling the need to start over again. Some people are naturally gifted and can easily learn a language with more explicit processes, though even then, they are reinforcing their learning with implicit.
That said, I wholeheartedly believe that if education in general shifted to the idea of implicit learning as the goal for all learning, with explicit reinforcement, rather than the other way around, it would transform learning as drastically as the industrial revolution transformed agriculture and economics.
It’s great that there is so much discussion about the importance of comprehensible and immersion learning and is the reason why I’ve always stopped - I never did that. I just lived in textbooks and memorised things quite robotically.
I think it works very well.