If your first reaction on witnessing a bug or seeing a bug report is “that’s impossible,” you are plainly wrong. Don’t waste a single neuron on the train of thought that begins “but that can’t happen” because quite clearly it can, and has.
I should print that and hang it on my wall because some days one needs to be reminded there are no impossible bugs, even when things just don’t make any sense.
On the flip side, I need a reminder somewhere that I should never let the thought, “But no one would ever try to do that,” stop me from testing for a bug. Because if it’s possible, someone will try it. 🙂