Ok, let's try and make a point.
Inter wants to win the Scudetto. Last year injuries and suspensions played a big role in our bad season. We don't want to be in that situation again. We're talking about Mihajlovic, so let's consider the defense.
We have Materazzi, Cannavaro and Cordoba who have to share 2 places in the team. We have Burdisso, a very promising young player, who could compete for a starting position, and Mihajlovic, an old experienced player, that can step in if the others are injured or suspended.
Now, of course every player makes mistakes. Burdisso and Mihajlovic situation is slightly different, though. They're not starters, so they will play less than the others. That means that all they do will count more: if they play well, they will get more chances to prove themselves, if they make too many mistakes, they probably won't.
It's a question of confidence, and trust from the coach and the supporters.