If a typical drawing is made up of 200 strokes, and each stroke has a 98% chance of being "wrong" and spoiling the drawing, then that would mean that 99.99999...% of drawings would be wrong.
(Nearly all drawings or paintings are built up of a large number of small gestures, and an error in any one of them isn't usually significant.)
I live with someone who's a trained draftsperson for art: this is a skill only peripherally related to what Bob Ross does.