For instance, You are trying to write a module that I wrote sometime back. But the module that I wrote does more than what you need. It couples to some framework, some database.
You found out that you could use my code, but the problem that you are going to bring in with that code is just too much.
This is the famous Gorilla-Banana problem:
You want a banana but what you get is a gorilla holding a banana and the entire jungle with it — Joe Armstrong