If you were 100% specific you would be effectively writing the code yourself. But you don't want that, so you're not 100% specific, so it makes up the difference. The result will include an unspecified percentage of code that does not fit what you wanted.

It's like code Yahtzee, you keep re-rolling this dice and that dice but never quite manage to get the exact combination you need.

There's an old saying about computers, they don't do what you want them to do, they do what you tell them to do. They can't do what you don't tell them to do.