Standing out isn't something very approved upon in Jonas's community. For Jonas it is something he is forced to do or has to do, not only because he is chosen. But because he now had real feelings and knows more about life than even the head committee will ever know. Sometimes standing out IS a good thing, but for Jonas's community, it could very well be a life sentence...
The first time Jonas is forced to be different is in the ceremony of twelve, the skip him in the number order. They went from 18 to 20. Everyone of course noticed it and everyone was wondering what was going on, and meanwhile Jonas was thinking to himself, "what had i done wrong?". Everyone thinks the Chief Elder had made a mistake but then she points our he had not been assigned, but selected. Well everyone is thinking, selected for what, well he is the next receiver of memory. He automatically know he's different.
Another way Jonas knows he's different is the fact that he has feelings and that no one else in the entire community besides him and The Giver has feelings. They don't know what death is and they also don't know what real pain is. They have everything protected for them. Everything is different for Jonas, which makes him different then the rest.
In conclusion, Jonas is really brave in the fact that he knows hes different and that the rest of his life is just hanging there in the balance and he doesn't know whats going to happen to him. He knows he can't go back to the community, and yet he is brave enough to leave... He knows he's different. He knows it very well. But I think that just makes him stronger as a person