When parents try to tell their coming of age kid, a frequent rebuttal is "YOU DON'T UNDERSTAND, YOU HAVEN'T BEEN IN MY SHOES" and then the kid storms off into his bedroom in a fit of undefined spoiled rage ... likely to listen to some shitty music and sob about how alone he is.

You know exactly what I'm talking about, and most of the time the parents are just thinking "that kid is a piece of shit, but I love 'em. Wish I knew how they could just see the bigger picture."

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k, so

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Imagine you're trying to talk to someone about politics, and then they use the phrase "YOU DON'T UNDERSTAND, YOU HAVEN'T LIVED IT."

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That person is sounding exactly like a damned teenager who needs to learn how to keep their hormones and feelings in check.

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Difference here is that you don't actually love the person. So your sentiment is simply "that person is a piece of shit. I wish he'd just pull his damned head out of his ass for one minute and realize how idiotic and self contradictory he's being."