In Wittgenstein’s Philosophical Investigations, he proposed a thought experiment that challenged the way we look at introspection and how it informs the language we use to describe sensations.
For the thought experiment, Wittgenstein asks us to imagine a group of individuals, each of whom has a box containing something called a “beetle.” No one can see into anyone else’s box. Everyone is asked to describe their beetle — but each person only knows their own beetle. [And] each person can only talk about their own beetle, as there might be different things in each person’s box. Consequently, Wittgenstein says the subsequent descriptions cannot have a part in the “language game.” Over time, people will talk about what is in their boxes, but the word “beetle” simply ends up meaning “that thing that is in a person’s box.”
Why is this bizarre thought experiment disturbing? The mental experiment points out that the beetle is like our minds, and that we can’t know exactly what it is like in another individual’s mind. We can’t know exactly what other people are experiencing, or the uniqueness of their perspective. It’s an issue that’s very much related to the so-called hard problem of consciousness and the phenomenon of qualia.