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.
And don't forget, that sometimes day dreaming about going to space, might be more fun, than actually going. It's not like you can touch it anyways.
My point is: Remember to enjoy your dreams. And 99% of the time let them be just that: "dreams".
> 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).
This is very important. I didn't figure it out until late in life, and wasted a lot of effort and money that could have been better spent.
When you want something ask yourself "why", then ask yourself "why" about your answer as well. Keep doing that until you hit bottom and its usually something like "so other people will think more highly of me."
Whenever you find yourself with "impressing others" as a motivation, ignore it. You'll learn to care less about what others think about you when you realize how seldom they do.