BBC producer John Nathan Turner took charge of Doctor Who in 1980 and by the time the series was cancelled in 1989, he had only just become determined to step aside and let somebody else take the reins. Personally, I think that whoever takes on the role of Doctor Whos showrunner should leave the job after a maximum of five years in order to let the programme be reinvented and prevent it from falling into a particular stylistic rut, and to stop the writing staff from becoming a closed group of usual suspects. Had John Nathan Turner left with Peter Davison at the end of Season 21, he would have overseen the programme for four years and had a respectable body of work on it behind him. He would have been quitting while he was ahead and letting somebody else take Doctor Who in a new direction. But he only decided to move on after Season 26 which ultimately proved to be the original series last, later musing that perhaps he should have resigned during Colin Bakers era. If John Nathan Turner did step down earlier, Doctor Who could have potentially continued for a long time afterwards because it would be continually changing as it had been since the 1960s. But partly because he stayed on for nearly a decade, Doctor Who steadily decreased in ratings and its quality fluctuated until its demise at the end of the decade.