I'm sure you've heard the question before - are you a pessimist or an optimist? The important thing to realize is that your approach to situations, whether pessimistic or optimistic, is in your hands. It is your choice whether to put a positive or negative framing on things, and choosing to be optimistic is often the most valuable choice you can make.
Take looking for parking, for instance. You might be going downtown, where parking is notoriously difficult, but unless you start off with the point of view that finding a space is possible and that you are going to try, you will definitely not get a space. Being optimistic does not mean unrealistic - I can be optimistic about my chances of improving my swimming while not expecting to go to the olympics.
Optimism is a framing, an approach, the lens through which you filter the world. If you fancy yourself a "realist" and say that an optimistic approach is too rosy, I'd say to you that everyone sees the world through filters, and that your choice of a "realistic" filter might be just a mask for a pessimistic approach.
By choosing to look at and for the positive, you create opportunities for yourself that others don't see, you recover more quickly from setbacks, and in general, have a much better time in the process. So next time, confronted with a daunting challenge or a bad day, remember that you can choose to focus on the positive, and that your optimistic approach is likely to be self-fulfilling.
Moshe Cohen teaches negotiation and leadership, mediates conflicts, and coaches people to become more effective with others.