High political and economic stability has brought us to this point. The more uncertain the world is, the more people prefer money today to money tomorrow. But when people have accumulated more wealth than they could concievably spend, and feel safe enough to let it out of their sight, they want to invest. Hence the flood of cheap money. The capital flight from China helps too.

Investors are also still believing that they can win the Apple lottery: buy an underappreciated tech company at the right time then watch it take over the world, and stay there forever.

I don't think we're in for a 'correction' any time soon. Where else are investors going to put their money? Leave it in a bank earning 0%?