If you look at the history,

Not every 16 year periods, Sp 500 achieved 12% annual return. And another danger is that when you take 12% out, if it is a down year ( of Sp 500), then you might have trouble to catch up for the later years.

If some one could be sure for 10% return, i bet I would go for it. It might take 25 years. Hhowever, it's still a good deal.