- Was working in a JS file for a website.
- Decided to move file into a folder for better organisation.
- Made folder, copied file into it.
- Spent 30 minutes wondering why changes weren't working, questioning my JS skills and life in general.
- Called friend asking for assistance, he's as confused as I am.
- Realised while speaking to him that I never deleted the file that was copied, and had been making changes to that the entire time.

Needless to say I was a little bit embarrassed.