I used to work with another dev who had memory problems. This guy *literaly* could not remeber what he did yesterday...
So, he was trying to change one of the password screens we had in the app. This was a really simple screen. Logo, password prompt, and two buttons. He worked on this small change for two days, but everything he did did not affect the screen at run time.
So finally, he gave up and called me to help him... I come over, and look at his code. It looks ok. I make a small change, and see what happens. Nothing. I think for a moment, and delete the entire screen UI elements. Run the app. Nothing happens - screen still the same.
Then I got it - he kept changing the wrong screen... for two days....
took me a whole 5 minutes to figure out.