You made some good points and gave some good information there JPSLotus.
However, I think you misunderstood me.
Firstly, I wouldn't necessarily agree that Schumacher 'knew' when to retire. I would be more inclined to say that he simply retired when he chose to, on his terms, and for his reasons. In saying that he 'knew when to retire', it would seem that you have labelled it as somehow 'right' or 'appropriate' because you agree with it and that it fits with a commonly chosen apparent set of circumstances for retirement.
When I said that IMO, Rossi shared a character trait with Senna and Schumacher, I referred to a trait that is a mix of dogged determination, focus, and not caring too much, if at all, what others think when that helmet is on. They all had controversial values and defended them doggedly. These traits have led to Rossi's extra-ordinarily long career in premier class motor-cycle racing. These traits may lead to other outcomes with other great racers depending on their values and specific circumstances. In his prime, Rossi was highly successful, but this trait has transferred into his determination to stay and to keep competing long after others would have stopped. Stoner (love the fella for his sincerity) said he was unhappy to see Rossi struggle because he was such a fierce competitor at the front.... a 'killer'.... i.e. relentless... yes.
Schumacher had the temerity to cheat in 2006 after so much success, a manifestation of the same trait in a different personality and circumstance. I'm a mega Schumacher fan and it took me a while to accept what he did and to see him as the complete and multi-faceted competitor that he was. In a not dissimilar spirit, Rossi has the temerity to claim repeatedly, that a championship was stolen from him!! As with Schumacher, I've managed to maintain my respect for Rossi as a great competitor and rider despite his flaws. Don't we all have them?
It was my in-depth knowledge and following of Schumacher, Senna, Prost, Alonso, Hamilton, and now in MotoGP and being late to the party... Rossi, Stoner, Lorenzo, Pedrosa, Dovi, Hayden and now, Marquez. All have their issues and for me, it's more rewarding to see them each in their full colours, rather than as in black or white.... Either as a 'can do no wrong' (denying any valid criticisms).... or an absolute '......' who is discredited in all ways.
I personally admire them all as great competitors and the more they are at the front, the more they will be the point of focus and the more their characters will be tested. There's a prize to be won and it's close. There are others in the way. Who will be provoked first? Makes for great entertainment! Unfortunately, Rossi's currently manifested show of determination isn't making for good entertainment. I do feel that he will finally stop this year.