I've had my 401(k) going since 1987 and it never "went bust." As you get older, you move more and more of it out of stocks and into fixed and balanced funds. In fact, I'm kicking myself a little now because at my age, I have a larger percentage out of stocks and thus I'm missing out on much of Trump's big stock market boom. But at my age, I'd rather be in the situation of protecting most of what I already have as opposed to risking it all.
After that, I did not want to risk my capital any longer and wanted to pretty much preserve what I had left. I should have pulled my money from the market in 2008 and put it in safe harbor somewhere. Coulda, woulda, shoulda, but didn't.
I don't worry about missing the run up on the stock market recently. Because there will be sell offs too where you will lose money. Better to not be too greedy when you don't have any income earning capacity left to replace the lost monies.
I saved my money after 2008 but didn't invest it. When I retired, I built a new house with the cash, paid off mortgages on two rentals and cleared the deck of any credit cards or misc. debt.
Now I have cash in the bank, no debt and a steady income. Am I wealthy? No, but it's calving season and life is good. :-)