It is quite okay to optimistic or even pessimistic but overall seeing things for what they are and being real about them is much better.
Too often we have unrealistic expectations of people and/or situations, which leads to heartache and disappointment. Instead of accepting things and people for what they are, we hold out hope that they or it will become what we want. The selfish self-centered person is not going have a epiphany and change overnight. So why waste time and energy hoping that they will?
We tend to set unrealistic and often unattainable goals and then beat ourselves up because we weren't able to achieve these goals. Be real with yourself, accept your limitations and in turn you will be able to build on them in order to achieve much bigger goals. So when you set out to lose weight, to become fit or landing your dream job first lay the foundation and them slowly and realistically add layers. Therefore, in time you will achieve what you set out to, without having unrealistic goals.
We have all heard the phrases "you are so optimistic" or "you are so pessimistic" at one point or the other in your life. I have to say I'm neither because I'm a Cynic; what you see is what you get. I set realistic goals for myself and I do not have unrealistic expectations of the people I come into contact with.
Be realistic in your expectations and goals and you will have realistic success and achievements.