Do you have any evidence this is actually recommended? If I leave $100k on the sidelines for 5 years and magically invest at the exact bottom of a 50% crash and double my money when it rebounds, how is that any different than having invested those $100k in the first place? At a 10-15% return, that’s basically the same returns (we can play with the 10-15% and 50% crash numbers, but my point stands).