Sometimes I'm told that a program has a bug. I trust the bug submitter, they are seeing a bug. But I can't reproduce the bug. I can't figure out what the bug could be by inspecting the code. I'm stuck. Much time is wasted.

Eventually, the bug submitter does a lot of work to help me reproduce the bug. I see the bug happen. Very shortly afterwards, I notice some peice of information that I hadn't paid attention to before, and I suddenly understand the bug, and can now quicly fix it.

It's not that reproducing the bug has helped me figure it out, it's just that some corner of my brain refused to work on the bug until I saw it happen.