As I am painting and then again when I am done I look at my painting in several different ways for form, values, etc.
I look at my item in a mirror for a mirror image, and I also turn my work upside down. Usually if something is not quite right it will jump out at you in viewing one of these ways. It is kinda like "checking yourself" when we were learning to do simple mathematical addition, subtraction, division, etc. Just a "making sure".....
When I am completely done I like to put the item on an easel somewhere in the house or prop it in an area that I pass by often so I can check it several times this way also.
You may want to lighten a highlight, darken a shade. emphasize an area, change the direction of a leaf, etc. before you call your painting "done".