You might think I am joking but I am not.
Take a look at the photo above. This is a scan of a living man’s brain: the black part is fluid, while the part around the black part is his remaining brain. Essentially 90% of his brain has been displaced by the fluid. And yet he was considered a functioning person, despite only have 10% of a brain mass most people have.
The story behind the scan and the questions that it raises is in this article: A civil servant missing most of his brain challenges our most basic theories of consciousness.
Fascinating. Perhaps in a few years / centuries we will understand how the brain works. For now we are mostly clueless, much like you are while you wait for your coffee to kick in. 🙂