John Travolta's career was made by playing Danny in 'Grease' - an entire generation fell in love with his song and dance act, and he was instantly one of the hottest stars in Hollywood. If you've seen 'Grease' - which we imagine is all of you - then you'll know it's about love, dancing, and teen culture in the 1950s. If there was anybody who should have known all about that it was Henry Winkler, who'd essentially been playing Danny 'Grease' had even been written with his role as Fonzie on 'Happy Days.'
The problem with casting Winkler as Danny was that it was too obvious, and Winkler knew it. He felt that if he went straight from 'Happy Days' to 'Grease,' then he'd have been typecast for the rest of his life, and would never be offered any parts outside of '50s rogue'. As his career trajectory turned out, he needn't have worried - he was never offered very many major roles after 'Happy Days' anyway. Had he known in advance that his career had already peaked, he'd probably have taken 'Grease' in a heartbeat.