Nope, not at all!
On the other hand, it is not a science. Most of the "rules" of drawing do not apply when you get down to it and start drawing, however they are not to be ignored, the rules ARE important. But not to work as they dictate, but to notice in which way they are wrong.
No one has ideal proportions. They are ideal, not realistic. It is up to the artist to decipher in which way a person defies the rules. Is he long-limbed, short, tall or portly.
A would-be draftsman needs to think about many things while he's drawing; proportion, format, color value, perspective, shape of t