A horse that refuses a jump usually has a reason: fear, pain, a bad approach. People who freeze usually do too.

A refusal usually has a cause, and the cause is rarely stubbornness. Fear of the obstacle, pain somewhere, an approach that arrived wrong: in each case the animal is telling you something, and punishing it only adds another reason to refuse. People lock up for similar reasons, and treating a freeze as laziness guarantees you never find out which one it was.

When somebody stalls, including yourself, ask what the reason might be before adding pressure. Check the simple ones first: is something hurting, is the fear specific, was the run-up wrong. Fix the approach instead of demanding the same thing again at the same speed.