Interestingly, he only appeared on the show because, as he bluntly put it , "I lost a bet to Matthew Perry.” Apparently the two had engaged in a bit of betting on the set of 2000's The Whole Nine Yards, with Perry arguing the film would be a box office hit , and Willis taking the opposite view.
The point about treating it as a trial rather than a payday is a good mindset. It makes the whole experience feel less like a gamble and more like a demo.