My code kept breaking on line 12 for 3 days, then a sticky note on my monitor solved it
Three days ago I was stuck on a loop that kept printing the wrong total, and I swore the math was right. I finally printed the variable in the middle of the loop and saw it was resetting to 0 every single pass because I put the line inside the loop instead of above it. I stuck a pink sticky note on my monitor that says "what changes every time?" and now I check that first. It sounds dumb but it saved my whole weekend. What dumb little check do you keep next to your screen?