Unfortunately most people won't do that, either from ignorance or fear of missing out. Sometime in the next few years the chickens are going to come home to roost on the infinibubble, and I'm not really sure if the US financial system will weather it.
VVIAX (Vanguard) or FLCOX (Fidelity)
to reduce your exposure to the highest of high-flying stocks.
Of course, many small company 401Ks limit your investment options to a small family of high expense ratio funds...