The process is very gradual, you see. At first there's the tainted stage; they know what will eventually happen to them if they go on but they say, 'Oh God, don't do it to me do it again, please, please.'
I love tennis with a passion. I challenged Boris Becker to a match once and he said he was up for it but he never called back. I bet I could make him run around.
I was well aware of the fact that once you appeared in Doctor Who as something else, you were ruled out for the part of the Doctor: that was a kind of well known thing in the business.