We have to distinguish "our" dreams from, let's say, cultural ones. A lot of what we want, what we perceive as living a full life, having fun and so on comes from culture (and increasingly in the last decades/centuries, with mass media).
Besides that, we can't achieve everything, we could not be everywhere when something interesting happens there, at the very least because a lot of those things happened in the past, or do everything because physical condition, economics, or extra conditions (i.e. being an astronaut).
So you draw lines. This is what I can do, I can go, I can be. You may push boundaries, but in the end it will always be more things outside than inside. And try to be the best on what matters on those boundaries.
Besides that, we can't achieve everything, we could not be everywhere when something interesting happens there, at the very least because a lot of those things happened in the past, or do everything because physical condition, economics, or extra conditions (i.e. being an astronaut).
So you draw lines. This is what I can do, I can go, I can be. You may push boundaries, but in the end it will always be more things outside than inside. And try to be the best on what matters on those boundaries.