Understandably, the more you draw a shape or a line, the more it settles into you.
That's the whole point of practice. Drawing involves a lot of memorizing, like any other study — but not cramming. The memorizing happens unconsciously, and it gets internalized.
I can't explain why some shapes and lines come more naturally than others. But one thing's certain: I must have drawn them far more often than the rest. I must have observed them far more often, too.
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