Effects of bit to small or to big?

What are the effects, and will it hurt the horse

im sure in some way it would hurt the horse, but i am not 100% sure.

The bit will not put pressure on the places is was ment to and will not give the correct signals to the horse. Small bits can pinch and big bits can be too loose and knock around on their teeth. For a bit to be used how it is made to be used, it must fit.

Too small will pinch.

Too large will be sloppy and not give the correct cues to the horse.

A little like wearring the wrong size shoes for a person, too small and it's very uncomfortable and painful, too big and it makes it hard to do things without having something else getting in the way.

Oh ok that makes sence. thanks!