Cash is a good way to lose money through opportunity cost:
* https://ofdollarsanddata.com/even-god-couldnt-beat-dollar-co...
If you're worried about risk and being able to sleep at night, you can dial back from 100% equities (S&P 500, Russell 3000), and do some bonds. Vanguard (e.g.) has funds that are fixed 80/20, 60/40:
* https://investor.vanguard.com/investment-products/mutual-fun...
This way you don't have to go through the effort of rebalancing yourself.