To give another side to our insight...
When the economy had problems in the 2007-2010 time period, I was laid off. Since I was approaching retirement and was trying to put as much money aside as I could, losing my income really caused financial concerns. Two years later, health problems and associated expenses took much of what I had put away apart from my 401K, as well as making it clear that I was now retired and would not be earning more.
I took that retirement fund away from company management and invested it thru an investment company. I diversified across several kinds of funds. Over the years, I kept watch and re-balanced between funds according to their overall returns. I did this at times when the market was fairly stable (not rising nor falling) since these are the times when overall returns are most clearly seen.
This had served me well and I have been taking disbursements to augment Social Security and making a few larger withdrawals when I made larger home repairs or changed cars, avoiding loans. Even after taking out a few% per year, my balance is many times the original value.
While others may have made more, I am satisfied with the results of the investment. I doubt that I would have done better buying and selling individual stocks or funds directly from the market.
I am not having the retirement I was planning before the economic problems (and my particular problems) The Lord has blessed me thru my investments, as well as in other ways. I value the opportunity the investment company afforded me.