It is a rare shoot or project that I come away from feeling that I nailed every aspect. Even when I have confidence from looking at a teathered laptop or chimping the back of my camera, invariably I see things that could have been better when I start my processing.
The worst kind of mistake for me are the settings or configuration errors. Sometimes these are inadvertent dial moves, and sometimes just sloppiness. Face it, there is a reason why so many people use a point and shoot, or even keep their DSLR in auto mode. The reality is that the camera will most likely make a decision on settings that are likely to work.