Hi, I figured I'd make a thread about this. What really blew your mind when you learned it or what continues to blow your mind when you think about it? I like learning really obscure mind blowing things so I figured I'd ask others about this to get some new ideas. For me it was things like uncountable/different "sizes" of infinity in real analysis, time relativity (it still blows my mind knowing most people go their entire lives not knowing time is not absolute) and currently things like fractional calculus. I think finding out you can take any order derivatives "Abusing" gamma functions and using certain integrals was ingenious. What is yours?