The SWEET EMOTION star, who rejoined the band five years later (84), was suffering from a well-publicised drug problem and was fed up with Aerosmith's unreliable behaviour letting people down.
He says, "There's a contract that you have with your audience that every band is sworn to.
"When someone out there works a nine to five job all week and they decide to spend the money that they've earned on your band then you have to deliver.
"Whether it's making an album or that person coming to see you in concert, you have an agreement with each other that they believe in you and you have to give them that reason to believe.
"At the end of the 1970s, we got really stupid and lazy. We were making mistakes that a band of our class shouldn't be making.
"We were breaking our contract with the people that believed in us and when you can't keep up your end of the bargain then that's when you call it a day and that's exactly what I did."