Can your belief affect the outcome of an event? Such as if you believe that the future will happen a certain way, will the outcome be what you believe?

Yes, though only in those limited circumstances where the believing itself brings about the truth of that which is believed. This mostly happens indirectly and the outcome is typically only partly explained by the belief (so it won't always work!). Consumer confidence, studied by economists, is one example of this: if enough of us lose our confidence in the economy that can, through its effects on our consumption patterns, bring it about that an economic down-turn happens. Positive consumer confidence can have the reverse effect. Single person cases include believing you can do something, which can give you the motivation and confidence to really throw yourself into the task and so make it the case that you can, when you couldn't have if you lacked that belief. Again, though, there is no magical guarantee: the belief has to work by marshalling sources of motivation and competence, which you might or might not have. There is an interesting, though even more limited, set of cases where the believing itself...