the key with investing for the most part is to just put money in every month and dont look at it. If you keep on putting in while the market is low, then you will get crazy return on that money and it should offset the losses on the other money. It makes me laugh when people see the market drop and they stop investing. That is the best time to invest. But the key is to diversify your money, you do not want it all in one place. If you have your money spread out, it is less likely to take a hit from a single occurrence. For example right now we have I bonds, roth IRA (Spread out), mutual funds (spread out), 401k(Spread out), TSP (tax deferred for government employees), and my wife's 50% retirement here in 5.5 years.
I know that we will never be rich, and it would be nice, but we look at things realistically. Once of my key points has been to try to retire without having any dependency on Social Security, because we do not believe that it will be there when we go to retire.
The main thing to do is to not go overboard. You do not want to not enjoy your life because you are saving... only to die young.