At the Ceremony of Twelve Jonas is awarded the very great honor of becoming the next Receiver of Memory. This is one of the most important assignments in the community and carries with it enormous responsibility. In fact, as the Chief Elder's speech makes clear, it isn't so much that Jonas has been assigned this role; it's more that he's been selected on the basis of a number of skills that make him the right choice.
And yet, for all that, Jonas is never entirely happy with his new position. For one thing, it provides him with an uncomfortable glimpse into the true nature of the society in which he lives, with all its evil and hypocrisy. It also makes him inadvertently hurt those closest to him.
For instance, he gives his sister Lily the memory of being an elephant, as a stuffed elephant is Lily's comfort object. But instead of being a pleasant experience this giving of memory ends up hurting Lily because Jonas holds on to her shoulders too tightly. As well as physical pain Lily experiences confusion as she has no understanding of what a real life elephant really is. It's at times like these that Jonas realizes that a Giver's lot isn't always a happy one.