When you perceive the world it is the extraordinary which the mind’s eye resists. The glint of light obscuring the eye. The distortion of the head leaning heavy on a fist : the angle of the neck. Logic wants to make these strangenesses and peculiarties explicit.
This is why to battle this normalising part of the brain it is useful to compare angles with verticles. Imagine your pencil is the big hand of a clock. Hold it up vertically up to the model. Find the angle of the arm. Is it at 9 o’clock ? Or 8? The world is particular.
There might be a part of you shouting. “Freedom!” I don’t want to draw like a conventional drawer. I want to sparkle with my own voice. That is fine but the left side of the brain, that bit that loves techniques has a terrible habit of making the world seem a bit ordinary