One example of changing beliefs that can happen daily is the belief that you completed your homework. You may have formed a belief that you completed it on a lie to yourself only to later find that when you look at the assignment its blank. This belief is changed without second thought because your entire belief was based around the content of this piece of paper. It is in examples such as this that beliefs are based around the state of the world that dont involve anything more than is observable that can be changed this way. This is that the belief is true if the world mathces what is expected and false if it doesent.