Fruit

"Here's the thing," I said to her, "Every fruit has some part you can't eat. Peach pits, banana peels, orange rinds. People can eat apple cores and lemon peels, I guess, but they don't. Even seedless grapes are served with the stem. Sometimes it's to protect seeds, but just as often it's not. Why is it, then?"

She thought for a moment before replying. "You know," she said, "personality flaws can be divided between those that are load-bearing and those that aren't. Load-bearing personality flaws are a response to a current need or situation. Maybe not the best response, but a response nonetheless. Sometimes the need goes away, and the flaw stops being load-bearing, and sometimes the flaw develops without a need - a chemical imbalance, for instance. The way to handle a load-bearing flaw is very different."

"Wait. What does that have to do with fruit?" I asked, irritated.

Then I realized I'd been talking to a theremin all along.