Why is it always the case when you give your cide to QA they find more bugs than you? Even though developers write test cases, why can't we catch them all?

As a the person who wrote it you have a certain set of assumptions that they do not. It's about that simple really.

True that. No one can catch them all. This is why we QA. Testing is not dirty word, crevice is a dirty word....

Simply because that's their job!! In theory, you should both be working from the same set of requirements, but they will just think about things differently. It's the same as 2 developers essentially implementing the same solution in different ways - different thought processes.

Because we're not Bug trainers?