When continuing beyond a point like this can actually make things worse, you move from diminishing returns to negative returns. This can happen when you are striving for perfection and it becomes counterproductive. There are lots of phrases related to this concept—overdoing it, trying too hard, etc. (see the Too Much ofa Good Thing section in Chapter 2).
Chapter:
Spend Your Time Wisely
Section:
You Can Do Anything, But Not Everything