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 the underlying object (plastic anatomy), angles, light sources (shadows), and sex (necessary byproduct of being a man, we cant turn it off ). Not many of these things are scientific. You use your gut feeling for the most part, but the gut feeling is only good when it is confronted with a specific problem. Drawing well is a test of concentration and intelligence and most of all constant practice! When you think you got it all mastered and stop thinking about one(or more) of those things, you duck up and there's something missing in the picture.
It is hard to completely concentrate on a task, especially one that takes as long as drawing. The brain gets tired and you make mistakes. The only thing you can do is improve its endurance by PRACTICE
But if you are a casual draftsman and you want to relax by drawing, like I do with my fantasy work, stop worrying and let your mind flow.... let your hand, not your mind do the work and enjoy the messed up forms you make