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Jonas needed courage the most because he had to "give up" a lot, that is, his identity as one like everyone else. He had to look at things he saw straight on even though it was very difficult. For example, he watches a boy die, after having received the memory of death/warfare. Jonas doesn't want to continue but he knows he does not have the ability to choose.
It took courage for Jonas to face the truth about the "release".
He was very confused, like in shock in realizing that "release" is murder. The Giver tells him that people live the way they do because it was already chosen for them.
Jonas, at first, isn't sure he made the right choice to leave.After he leaves their community he is virtually starving. He is cold too. Although, in his wisdom, he realizes that if he had stayed, Gabriel would have died. So, he thinks that, in a way, it wasn't his choice after all.