Your life is what you do with your attention
Your life is a string of moments. In each one you're choosing to pay attention to something or something has grabbed your attention. Whatever you end up paying attention to is exactly what makes up your life. From your point of view there is nothing else.
You can control your attention and therefore decide what your life is about.
The pessimist and optimist experience two different worlds. Their habitual judgments shape the nature of their experience to be worse and better—determined by what they pay attention to in each moment. The pessimist notices more negative things in his environment and so subjectively is in that worse environment. If he thinks everyone around him is an asshole when they aren't, he's having exactly as bad a time as if everyone truly was.
It's not about how much time he spends around all these annoying people or situations. What matters is how much of his attention is taken up by thinking, worrying, complaining, and stressing out about these things.
The things I do that are enjoyable, satisfying or meaningful are not this way because of what I am doing but because of the attention I bring to them (Presence is a better proxy than happiness for meaningful moments). Consider that meditating is rarely boring. Boredom is a completely internal condition that doesn't doesn't have to be related to the actual activity. The things I enjoy doing the most are the things that I bring my full attention to and that invite me to do the same.
What you see is all there is. What we see is determined by what we pay attention to. Most of the time our attention is constantly grabbed, but through direct practice—meditation—you can take more control of your attention and therefore your life.