He was good friends with the Mozart family until 1778 when the Mozarts broke off their friendship because MysliveÄ ek promised , but then did not arrange for Mozart to write an opera for the theater in Naples . He was close to the Mozart family until 1778 , when contacts were broken off after he failed to make good on a promise to arrange an opera commission for Mozart at the Teatro San Carlo in Naples . Earlier , the Mozarts found his dynamic personality irrestisible .