2008 was a very unique recession and severity in recent memory. I have made a statement in one of my posts, I have said that we will not see another 2008 in our lifetime, or I should say that the chance of another 2008 type of recession is almost zero. The only recession more severe than 2008 was 1929 called Great Depression.
Why I am saying that we will not see another 2008 recession in our life time? 2008 is a perfect storm, every bad things happened at the same time. Put it simply, before 2008, a insurance company sold a lot of life insurance to a lot of people and think that not everyone will die at the same time. But in fact, everyone died at the same time in September 2008, the insurance company does not have enough money to pay everyone and the company went bankrupt. That was what happened to our financial systems.
That said, recessions are part of our economic cycles. I am 100% sure that we will have one soon, but I don't know when. Based on recent history, nine of last ten recessions happened during Republican Presidency, so you can figure out yourself.
During 2008, there were a lot of 401(k) portfolios with 50% paper loss. I would think that everyone's investment portfolios with 100% equity market allocation lost 50%. The key here is age proper asset allocation. That is why we will need to have total stock index fund with 1,000 to 2,000+ stocks in the fund, the risk is more diversified. Individual stocks are more riskier than sector funds (100 stocks), sector funds are more riskier than S&P 500 Index (500 stocks), S&P 500 Index is more riskier than Total Stock Market Index (1000 to 3000 stocks). As we are getting closer to retirement, we need to allocate more money to bonds or bond funds. 10%-20% in your 40s, 30%-40% in your 50s, 50% in your 60s.