It's the sort of thing you either "get", or you don't. If you get it, you've got it, and if you don't it can't be explained to you. It's like breathing or football.
The most common thing I've heard this in reference to is Jazz with second runner up being religion. Sometimes it's used as a cop out to get out of what might be a tediously boring discourse, but most of the time it's inherently true: you have to come to the meaning yourself, or else there is no meaning to be had.
"What's so great about having a computer in your car?"
"If you have to ask the question, you wouldn't understand the answer."
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