Be it marriage, business, team sport or any other enterprise involving more than one human being, the biggest ingredient for success is trust. Ruthlessness is fine but it is a managers job to keep people motivated and on board. That involves having to accommodate everybody involved. If for whatever reason that promise is given, then that promise has to be kept. Not only if possible, or maybe, or if the circumstances are right, but at all costs. If not then that is the slippery slope of losing the confidence of everybody that has any dealings with you and you find yourself in the same situation that Mourinho finds himself in every 3 years at every club he goes to. It goes beyond football and to the core of what it means to be a good, decent and honest human being. Given the choice of a Mourinho and a Pellegrini, it'd be Pellegrini every time. I would be willing to bet that Pellegrini, whatever you think of his abilities as a manager, has the full respect of everybody at the club.
He certainly has mine.