The systems analyst, software designer and acceptance engineers often ask: "What did they do that for? Who would have thought a pilot would do that?
Ian W, I knew a programmer who worked for a company making smartcard compatible washing machines for laundromats. He was the go to guy, that the company sent software to, in order to get the bugs out. He told me the biggest problem, was just as you say. For instance: His fellow programmers would ask questions like "Why would anyone open the door, before the cycle ended? That wouldn't make sense." And they wrote the software accordingly.
Go ahead and convince yourselves, if you want, that there is not a programmer of some obscure, hardly used subroutine in flight control software, that didn't use that line of thought while writing it, since it's more important or more glamorous than washing machine software.
Thankfully, most of these bugs are uncovered with thorough testing.