” We waste away dwelling on it, not knowing if what we have dreamed of can become a reality someday “

The only statement made by Dumbledore I don't agree with.

I believe if one has such a dream, regardless of whether it can become a reality or not, one must begin striving to make it a reality. Even if on the way it becomes clear that it will only remain a dream, something else would have been realized. Something else which wasn't as good as what one dreamed of but something good enough. Soon you realize that what was realized instead that which was being pursued, has made you happier and content than what you'd dreamed about.

That is where a person wins.
After all, you make it to the sky, only if you aim for the stars.