Sticking with an "easy" index investing strategy involves a deceptive amount of decision making that will impact your returns over a long period of time.  Even if you only invest in one index fund you have to make the decision when to contribute your funds and have a deep commitment to continue contributing to the fund over a long period of time.  I suspect few people possess the ability to make good decisions on either front.  If this was simple and easy everyone would retire with multi-million dollar accounts.