Warning: my first bug took me 5 hours and it was a missing quote mark
Last Tuesday I spent 5 hours staring at my little Python to-do list script that kept crashing on line 14, and I rewrote half the file twice before my buddy Dave looked at it for 30 seconds and pointed at a string with one quote mark missing. I had been reading error messages about an unterminated string for hours and somehow my brain just skipped right over them. Five hours. For one character. I closed my laptop and went for a walk around the block after that. What was your dumbest little bug that ate a whole afternoon, and how did you finally catch it?