We do not live in the wizarding world. There is a limit to how much your perception can influence your own body, or physical processes around you. That applies in both directions - belief alone can't move a mountain, but it also can't stop the excavators already moving one.
I would argue that because your body is the one doing the perceiving, there is likely no limit to the ability of our perceptions influencing our bodies. Belief alone can't move a mountain, but is that not because the belief is not strong enough, rather than because beliefs don't physically have hands with which to hold the pickaxe?
