Belief is the decision to think something is true, whether or not it really is. Believing something is true will not make it true (if it is not already true), but it will align you with reality if it is true, and will steer you away from reality if it is not. Because reality has a way of imposing itself eventually, the wise person who wishes to avoid unnecessary trouble will continually question his or her beliefs, seeking to be guided by what is true, rather than by what s/he believes (what s/he (mis)perceives to be true).
Belief can also be the decision to think something could be made real, or made to come true, even if it is not currently real or true. This is belief as a creative force, rather than belief as a personal (mis)perception of reality. Whether or not something really is, now, does not necessarily mean that reality cannot be changed. Looking for, recognizing, and accepting current truth is better than dealing in fantasies, which will only lead to trouble. However, believing that things could better is better than thinking that reality cannot be improved.
Sometimes, things are just the way they are. Other times, "it has always been this way" does not mean it can't be another way tomorrow, or today.