Sketch: character expressions

I keep trying to doodle out character sketches on large sketchbook paper and I always don’t feel like the ideas flow easily. Give me a stickynote pad and I’ll sketch like a madman.

I think it’s the “permission to make a mistake” thought habit. A good sketchbook makes me think thatevery page must be a masterpiece or a good quality sketch. But not a place to play and make mistakes.
The art classes ive taken didnt help by making sketchbooks something to submit projects in.

In a creative writng class a teacher had us buy a notebook to free write in and we would never be required to turn it in or show the teacher. A place to freely make mistakes.
I need to find a way to make myself think this way with sketchbooks.