Beliefs are filters. A belief is like an item of clothing, you can put it on and take it off. Put on a belief and that is how the world will look, take it off and the world will change. A sorcerer uses beliefs as tools, putting them on and taking them off at will, allowing them to see reality through different lenses, each with their own advantages and disadvantages.
Non-sorcerers think that because the belief makes the world look a certain way, it must therefore be true. This is a mistake. They are seeing reality filtered through the belief. For example, if you wear yellow-tinted glasses, everything is yellow.