Probably because we have the obsession of making them look perfect to our specifications. Otherwise, if we screw up even once we feel unsatisfied and start all over again.
Somedays the connection between the mind and hand can feel unreliable, often feels like trying to figure what will appeal to ourselves to get even line placed down is a puzzle where the solution changes on a whim
Comments
I'm afraid of messing up even one bit of detail when I do fanart, especially VTubers.
I am projecting a tad, admittedly.