There is a scene in the movie where Astrid and Hiccup fly on Toothless's back toward the island of Berk. The animation is intensely real, from the waves on the sea to wisps of wind blowing in the characters' hair. The feeling I get watching that scene is why I fly - just for that feeling.
Changing the world is good for those who want their names in books. But being happy, that is for those who write their names in the lives of others, and hold the hearts of others as the treasure most dear.