This morning, I was trying to figure out why one of our customers couldn't upload a picture to her website. She was using a form I had built, so fixing the bug was assigned to me. After some digging around, I found out that the problem was actually in another programmer's code library that my form used.
"Rookie mistake," I thought to myself. "He forget to lowercase the file extension." What that meany was that someone could upload an image called "test.jpg" just fine, but "test.JPG" would fail.
I fixed the bug, chuckling smugly to myself, then went back to my form to try uploading the picture again. It failed. What?! As it turns out, I had made a mistake even more rookiesh in my own code, trying to display the new picture BEFORE actually uploading it. Oops.
It's incidents like these that keep me from getting too cocky.