We often limit ourselves because we don’t think we can achieve something. Today it may be hard for you to imagine that you can live without dessert or that you can live below your means. It doesn’t mean it’s impossible, though; it’s only your subjective opinion, not a fact of life.
Moreover, thinking that you’re unlikely to win means that you’ll put in less effort than you could. Why would you work your fingers to the bone if you were uncertain of success?
Rock climbing has made it particularly clear to me. When you approach the route thinking that it’s beyond your abilities, you won’t do your best. After all, why try your best if you know that you aren’t going to climb it anyway?
You’ll most likely give up when you encounter the first obstacle, while a person thinking they can climb it will fight as hard as they can to keep climbing. In the end, the person that doesn’t believe in their abilities will give up along the way while the person that is certain of their abilities will reach the top.
Periodically try things that you think are outside of your ability with a positive attitude and the belief that you can succeed. Chances are you’ll get a positive surprise and achieve something you thought was beyond your reach.