You have to be willing take some risks and down years to be an investor. We also will likely see reduced returns going forward if liberals continue to run the government. Of course markets did decent during the Obama years so one can never tell.
Best strategy is to invest 10-20% of your paycheck over decades and leave it alone.
For many folks the investing of 10-20% of the paycheck has already been done, and they are now retired.
They will not have enough time to recoup losses incurred in down years.