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Likeness is harder to capture than poses. Humans are better at discerning details of the face to differentiate one person from another. It's much more difficult to draw likeness from imagination.
For me, I feel like my brain tricks me into thinking I see an image of a person or their face, but when I try to draw them, I realize it's not actually very clear what they look like. It will probably take hours of erasing and redrawing the same lines to get the likeness approximately, but at that point I am just guessing where the lines go until all of the lines look like what the person looks like.
The only way to actually draw someone from imagination is to try drawing them from imagination without reference, then correcting it with a picture of them, then trying again and again until you get it right.