This was taken from Harry's signature as I don't quite understand it.

How, exactly, can we know ten thousand things from one thing?

For that matter, how can we even know two things from one thing?

OK, I can see how we might know three things from two things (if the two things can be logically conjoined to produce the third) but you could argue that the third is already implicitly known when just the two things are known.

So then, Harry (or anyone else), care to explain it?