Nice 6% ROI you pulled out of thin air. Where exactly do you find that? It's hard to find a risk-free way that just keeps up with inflation at this point.

With the standard caveat that past performance does not guarantee future results, the historical average real return on the stock market has been >~7% [1, 2, 3, 4]. Assuming someone starts saving for retirement at a young age (say, early 20s), assuming that the average return will be close to the historical average is not unreasonable.

[1] http://www.simplestockinvesting.com/SP500-historical-real-to...

[2] http://www.istockanalyst.com/article/viewarticle/articleid/2...

[3] http://www.getrichslowly.org/blog/2008/12/16/how-much-does-t...

[4] www.ssab.gov/publications/financing/estimated%20rate%20of%20return.pdf

Well, 6% is the historical average including victory in a war that eliminated almost all of the US' global competition, the discovery and near-depletion of easy petrochemical energy resources, and major technological advances driven by the cold war/space race. Plus endless borrowing and debt expansion. It seems unlikely that the resulting 50 yr period of prosperity can and will repeat over the next 25-50 years.

I was going to argue that you can always invest internationally, but even this looks slightly dodgy.

The MSCI world index has had a 3% annualized return after inflation since 2000...which is strange and somewhat hard to explain. Another problem is that for the last 10 years, the best investment opportunities have only been available to rich people, at least in the US - the IPO market doesn't exist anymore and most wealth seems to be created in companies that are privately held.

I'd give my left nut to be able to invest in any company in the world.

If you start at age 18, you're likely to live through a couple economic cycles and it'll even out.

6% ROI's have long been dreamland (As real interest rates rarely approach that).