The guy next to me in a Denver coffee shop asked why my loop never ran once
I was stuck on a Python while loop for 2 hours at a place on 16th Street, and the guy at the next table leaned over and asked why I never changed the variable inside it. He showed me his own screen, a tiny script that printed 1 through 5, and said "if nothing changes, nothing changes" like it was the most obvious thing in the world. What is the dumbest bug you have stared at way too long before someone else spotted it in 10 seconds?