So investing at the seed stage is random. I'm surprised that VCs don't help new companies more in the early stage to mitigate some of the common failure patterns, for example the list PG had in 2006. Perhaps couples counseling for YC founders? Every little bit reduces investor risk even a little.
"Engineered random". Sam still gets a better deal flow than most of angel investors are out there, so even "meh" companies with high risk have passed some initial filter.
Any angel investor without the name or brand recognition gets much worse deal flow plus the companies subject to negative selection bias, as they've been rejected by sama, SV Angel, YC, etc.
http://www.paulgraham.com/startupmistakes.html