Will Hepburn writes a good piece about the cost of being out of the market on the best and worst days. You should take a look at the numbers. I think you may be surprised at the results. It was an aha moment for me when I realized if you were missing some of the best days because you had gone to cash, you were probably missing some of the worst days as well. Since the best and worst days seem to happen together.
Thanks Will for the great explanation. You took something complex and made it usable.