the purpose of optimism

[pokerchap]

hey everyone,

I read and post a lot and really love the psychology forum because the ppl arent dicks like most other forums and there is some good stuff in here that isnt only poker related

anyways, I am a HUGE pessimist because I dont understand the point of being optimistic, especially in poker. I dont understand how saying " im gonna win this tourney" really helps you win. Whether im optimistic of pessimistic it doesn't affect my play. I know a lot of ppl will say " you think its not but it is" this is not the case. In sports too. I really dont understand how thinking in my mind that i am gonna lose to a certain team affects the outcome. I still play hard and do my best.

I just dont understand how being optimistic changes things.