True Story: I've been assigned a data analysis task at work. Based on an ancient (4 years old!) email chain that happened to get re-forwarded to me, I saw that I had apparently written software for this very task in 2008. I do not even remember doing that.
A search of my hard drive has turned up some supporting software, but nothing like a "main" file. And the files were in unexpected locations - tiny subfolders with obscure names, nothing to indicate they contained analysis code.
Hoping against hope my 4-years younger self had a clue, I hauled out my lab notebook from 2008 and flipped to the spring.
"Data by hand: "
"Data by automated analysis: "
SELF! What program? Located where on your computer? HOW DID YOU DO THE ANALYSIS?
Notes. Good ones. Take them. *facepalm*