As sane of a suggestion that is, SPY index fund dropped a huge amount because the whole market dove. Not everyone can plan on suddenly missing 20% of their savings.
for retirement savings, balance should shift to bonds or similar as you near retirement.
same principle applies to saving for other large events, like a down payment on a house. decrease risk as even nears.
no need to manage this yourself; every roboadvisor will do this for you rather cheaply