I then start tinkering with the function, and all the while the problem is actually that i'm not even calling it.
Before I started programming, I kept hearing about how typos are the programmers bane, but nobody mentioned this. I don't know about y'all, but remembering to call a function I just wrote is my #1 mistake; typos aren't so bad, mostly because half the time it's a compile-time error.
Closely related is when I don't bother to comment or remove functions I'm no longer using. I'll come back a month later and tear my hair out trying to figure out what that function does, until I eventually realize it doesn't do anything. AARGH!!!