Normally, when a word in Japanese means two opposite things, the meanings depend on whether it is used in a positive or negative sentence. However, that doesn’t seem to be the case here. I am wondering when this word means “previous” and when it means “future”.
In the reprise of the chorus, it seemed like “遥か先へ進め” should mean something like “advancing far into the future”, not into the past. The lyrics translation seems to agree. However, the translations that I see of the first occurrence of the chorus with a different particle “遥か先で” just seem to be like “far away”.
Anyway, in “遥か先へ進め”, the word 先 clearly does not mean “previous”. However, in general, I can’t tell when 先 will mean future versus previous (or when it means something different entirely). Just pairing it with various particles and putting it into Google Translate offers no clarity. Wanikani’s example sentences don’t offer clarity. Does anyone have any hints?
Those seemed to focus on different usages, including position. Maybe, さき is a word where, when not relating to position, every single collocation just needs to be memorized to know when it is referring to the past or the future from a particular reference time.
Oh… 先… It took me several years to get used to it. Until then I was just ignoring it whenever it appeared and avoiding using it at all costs, lol.
I do remember after six years of studying Japanese (5 back at home and 1 in Japan) being asked by a Japanese beginner what 先 means and being “oh… that… nevermind…” to what they were all “No, I’m serious, please teach me” and I could only answer “And I’m dead serious I don’t know how to answer that. Please don’t insist.”
These days I use it normally, but I don’t really know how to explain it in a nice way. Just that, as @Leebo said, it’s definitely not exclusive to Japanese. Time expression are a huge mess more often than not.
No, I don’t have any useful advice or explanation about 先 to give you. I just saw an opportunity to talk about a past trauma and took it, sorry.