What I really mourn is the death of the pension. Sure, I have a 401(k), but I can drop all the money in the world into it with employer match and if the market goes bust, boom. No retirement. I do not trust the market enough to trust I will have a valuable retirement fund in 40 years.
The market will go bust and it will go boom again. It's this simple: in order for the market to have participants, the market must enrich investors or they won't play. If the average investor didn't make money in the market long-term there would be no market. Long-term, the market will go up, it's just a matter of the term. These are beta gains. Alpha gains are increases in investment due to idiosyncratic performance above and beyond the basic (beta) gains of the market. Beta gains are cumulative. Alpha gains are zero-sum: any money you make is offset on the balance sheet by losses for someone else. You can lose all your beta gains and more through alpha plays. This is why you shouldn't day-play your 401(k). Putting it in the market, however, does not mean you will lose it.