One nuance is that some parts of correctness may be negotiable. If I'm writing a file backup program, it absolutely must back up all the files without leaving

One nuance is that some parts of correctness may be negotiable. If I'm writing a file backup program, it absolutely must back up all the files without leaving any out or corrupting the data. But let's say it has a feature that prints progress indicator percentages on the command line, ranging from 0% to 100%. Maybe under certain circumstances (like files added to a directory after the backup starts), it prints 102%. It's not what I had in mind, nor is it something I'd call correct. But if fixing it complicates the code a lot, maybe leaving it that way is the better choice. (This is a bit of a contrived example because you could just clip the value at 100, but you get the idea.)