Because it's the smart thing to do.
For real. It seems that the trickiest bugs that I have encountered are the ones that don't throw an exception in your face. You get so used to your own code that you kind of just assume that everything has been typed correctly. Sometimes that isn't the case.
I've been trying to fix a bug related to my silly ice bergs not relocating properly. Basically, after they relocated, a boolean was changed to true saying that they are currently respawning, but when they passed a certain value on the x axis, this is changed to false. However, instead of checking the ice berg array, I was checking a completely different array. Rookie error.
I don't know; the code works now.