The free version of my professional thoughts on this broad subject came out this week. If anybody wants a link I'll gladly share.
The research data says otherwise. The biggest issues in personal finance are not the investment choices per se. They are dealing with the bad markets that inevitably come, issues of risk need and risk capacity, asset location, spending priorities in retirement and the like. You may be different (the research data also is clear that almost everyone thinks s/he is in the "different" category), but most people would benefit a lot with good, professional advice.
Diversification among indexes is as important as diversification among individual securities.