Because my work tends to have me working on a wide variety of features, and thus operating on vastly different parts of the codebase, I make it a point to comment out every change I make complete with the ticket that requested the change, and what the intended effect of the change is.
Cue me returning to piece of code I made (after the inevitable bug has arisen) and me staring at my own code changes in bewilderment, wondering what past me really wanted to do. Hahaha!
My comment is self-documenting, I swear!