Simply put, you can always find problems if you're looking for them. The tricky thing about writing is that there is no one right answer. There are countless possible answers, and sometimes to choices are equally valid.
This phenomenon leads to what I call circular editing. You read a passage, make a change, and then when you read that passage again, you change it back to the original. This can go on and on, cycling back and forth though that same passage.
If you are looking for things to change, you can always find something. But if you're wanting to take passages and make them better, then you may reach a point where you can't - you can only make them different.