How we cite our quotes:
"I felt sad today," he had heard his mother say, and they had comforted her.
But now Jonas had experienced real sadness. He had felt grief. He knew there was no quick comfort for emotions like those. (17.10-11)
It looks like everything is relative; Jonas thought he knew sadness and pain before he saw the intensity of the sadness and pain in the memories he received.
"Asher," Jonas said. He was trying to speak carefully, and with kindness, to say exactly what he wanted to say. "You had no way of knowing this. I didn't know it myself until recently. But it is a cruel game. In the past, there have – "
"I said I apologize, Jonas."
Jonas sighed. It was no use. Of course Asher couldn't understand. "I accept your apology, Asher," he said wearily. (17.37-39)
It's fitting that Asher ends the argument with empty words, when what Jonas was trying to do in the first place was get his friend to recognize how hollow his actions and words were.
The Giver shook his head and sighed. "No. And I didn't give her physical pain. But I gave her loneliness. And I gave her loss. I transferred a memory of a child taken from its parents. That was the first one. She appeared stunned at its end." (18.34)
The Giver, because he loved Rosemary, didn't want her to feel physical pain. But his decision to give her emotional pain instead may have been even more destructive.