Studying a picture and redrawing it from memory afterwards is not as easy as it seems.
I noticed you need to draw an object several times from almost the same angle and understand its construction, its form, in order to be able to reproduce it from memory.
I’m always trying to spot mistakes and weak points so I can be more careful on those next time.
I was always asking myself why every anatomy book insists on reducing human figure to basic geometrical shapes, I thought drawing a leg that looks good is enough. But I guess it isn’t, since you still need to understand which way is the knee pointing, if you need to add some armor to your character.
Also, starting with drawing a box and a few cylinders is a lot easier than trying to draw the whole hand without even understanding its shapes.