I think the point of putting retirement money in an index fund is that you are basically in the same boat as everyone else. If the economy stagnates for 30 year

I think the point of putting retirement money in an index fund is that you are basically in the same boat as everyone else. If the economy stagnates for 30 years and your money hasn't grown during that time, the same is true for everyone else so your buying power has stayed the same. If there was some kind of market catastrophe and you lose 90% of your money, again everyone is in the same boat as you so at that point you are probably looking at some form of government intervention to keep you whole. On the other hand if you put your money in some alternative assets that didn't do so great and only returned 20% while the S&P returned 1000% over that time then you are really in a bad situation that no one is going to help you out of.