Trust me, I am not very bright. But as boy with a 486 in the mid 90s, I was so inspired, a that I figured this out without the internet (was still unheard of) or the books.

I still remember the rush that I got when I got the rotating cube in my QBasic IDE in my 14inch monochrome monitor. The intuition I used was derived from how light casted shadows of 3d objects in a 2d wall..From there, this x' = x/z y' = y/z, follows naturally..