Also, learning the structure …し、…し to list non-sequential statements. For ages, I thought people were finishing all their sentences with し for no reason, and assumed it was some kind of slang particle.
Similarly with かな to express wonderment or のに to express disappointment. If, like me, you hear more Japanese than you study, you go through several phases of understanding with this kind of thing.
First 10 times you hear it:
I thought I understood what you said but then you made this random noise at the end…?
OK, there seems to be a tone of voice / facial expression you’re doing too. What’s up with that?
Over 100 times:
I sense a pattern of mild (disappointment/surprise/anger/contentment/excitement). I’m going to copy that and watch your reaction.
After a few attempts:
The results are inconclusive. Am I talking like a girl? More data is required.
Finally you look up a grammar lesson:
Gah! Why did nobody ever explain this?