You're standing at the beginning of a path, about to begin walking along it...
・The path {"in front of" / "ahead of" / "before"} you already existed prior to you having taken the first step (past).
・The path {"behind" / "following" / "after"} you doesn't exist yet—it will come into existence only if you start walking along the path to create it behind you—and it will won't reach its completed state until you reach the end of the path (future).
The path "ahead" might sound like "future" and may be what you'd use 先 for, but in a strange way it's possible to think of it as "past" instead. The act of walking down the path ahead is something that will take place in the future; the path ahead itself was there before you started walking it.
Just my thoughts about this. Likely not the correct way to think about it as this is completely made up stuff off the top of my head... :P
June 9, 2016 at 7:22am