Everyone has a sealed box they call 'beetle' — and the word can't mean what's inside

Wittgenstein imagined a community where everyone has a private box, calls whatever's inside it a 'beetle', and can never look in anyone else's box. Since each person only ever learns the word from public use, not from comparing contents, the actual thing in the box plays no role in what 'beetle' means. He used this to argue that words for private sensations like pain get their meaning from shared, public use, not from pointing at some inner object only you can see.

— Ludwig Wittgenstein, Philosophical Investigations — §293, 1953