Back in the 70's when Star Wars was shooting, George Lucas was convinced that his movie was going to flop. He went to visit Steven Spielberg who was filming "Close Encounters of the Third Kind". After seeing how Spielberg's movie was going….the sets, the production, the promotion, etc., he ended up betting Spielberg that Close Encounters would be a bigger movie than Star Wars. The two bet 2.5% points on the box office returns of each others' movies. Spielberg revealed in an interview with Turner Classic Movies that Lucas still pays him on that bet to this day! That works out to a $40 million pay advantage for Spielberg.

Here's Spielberg talking about the bet: