The worst feeling it is possible to have as a programmer is when you're testing something, and you make a change, and it doesn't fix the problem, so you make a change in a printf to test if you're running the right exe version, and it runs and prints the *old* printf, and you're like aha! I've fixed the problem! It's running an out of date exe! And then you go to fix that and you discover you can't figure out why it's running an out of date exe or how to make it stop