My finance professor suggests Buffett profits by being able to borrow cheaper. Sure, there's smart picks, but if you can widen the difference between the rate you're borrowing and your returns, your average returns increase. Here lies the unfair advantage - you can't compete with Buffett unless you can borrow at the rates Buffett can.
There's also the argument for diversification - investors holding large fractions of their portfolio in one security expose themselves to the operational risks of the company. By holding a broad variety of stocks, you'd expect their "lumps and bumps" to even out on average so you are only exposed to the overall market risk (i.e. hold airline stocks? Offset that with some oil stocks. And those with solar. etc.).
Nvest looks cool, but also seductively simple for the casual observer. It helps pick individual stocks, not necessarily build a balanced portfolio.