When you're helping someone with a bug for ages and then try something random and it's miraculously fixed so you have to spend another hour figuring out why...

Actual conversation:

Coworker 1: "So what did you do?"
Coworker 2: "X."
Coworker 1: "But how did you know that would fix it?"
Coworker 2: "Without X it doesn't work."
Coworker 1: "So why did you try X and not Y or Z or A, B, C or D?" (basically an infinite number of other possible fixes; this is a workaround for a hardware bug we found)
Coworker 2: "Well, without X it doesn't work, but with X it does."
Coworker 1: "..."