All of my nieces and nephews learned the meaning of that phrase from me. I am a wonderful aunt and without fail they used to run to me and tell me the woes of being a child of their respective parents. As they would whine to me about their complete list of injustices commited by mom or dad or both they would look to me for support and ask "why, do I have to suffer so much?" - or some such variation of the question.
My reply without fail was always, "it builds character." I said it so often that the kids would usually answer their own question with sing/song sarcasm "I know, it builds character."
Now that they are older I intend to ask them how they feel about all the character building their parents engaged in. I bet it gets a laugh.