We love a bit of sportsmanship, especially between some of the biggest (and wealthiest) movie directors of all time.
Back in the day, when Spielberg and Lucas were the undisputed kings of blockbuster movies, they would take out full page ads (with some brilliant artwork) in Variety, congratulating the other on surpassing them in sales.
A full page ad, taken out by Spielberg when Star Wars eclipsed Jaws in rentals
A few years later, E.T. became a mega-hit and Lucas returned the favour.