Harry Bailey is handsome, athletic, popular, and lucky. He might be a college grad and war hero, but he owes lots of that to his brother, George. As a kid, Harry accidentally crashes into an icy pond while out sledding. George rescues him. George gives Harry his college savings when George is forced to stay at home and run the family business.
George assumes that Harry will end up taking over the Building and Loan when he graduates, but instead, Harry gets married and has a great job opportunity with his father-in-law in another city. He's reluctant to take it because he knows he owes George big time:
HARRY: George ... about that job. Ruth spoke out of turn. I never said I'd take it. You've been holding the bag here for four years, and ... well, I won't let you down, George.
Deeply disappointed, George is still supportive and insists that Harry pursue his dreams.
George can't serve in the war because he lost his hearing in one ear saving Harry on that winter day. He stays in Bedford Falls, helping on the home front and acting as an air-raid warden. Harry flies a fighter plane for the Navy and shoots down 15 enemy planes, including two that were about to crash into a transport boat full of soldiers. He wins the Congressional Medal of Honor. Of course, none of this would've been possible if George hadn't rescued Harry when he fell through the ice. Clarence shows George that.
Harry has been the protected little brother throughout the film. He idolizes George; he knows he owes his life to him. He knows how much George has sacrificed. At the end of the movie, Harry toasts his big bro:
HARRY: To my big brother, George, the richest man in town!
Like George, Harry knows what's really important.