Investing it in other assets can be problematic when the global macro environment falters because you won't be the only one trying to liquidate!
It's not hard to imagine a scenario where the stock market and risk assets in general crash, and then you get laid off.
During a market downturn money flees to safety, bonds appreciate, stocks fall, and when you rebalance back to 90/10 you'll effectively be buying stocks at a discount.
The 100/0 guy has no such option and misses out entirely.
Not true. The 100/0 guy can buy stocks during a downturn just as well as the 90/10 guy. If we're really talking long term, that is, if neither person is selling, and if both are investing the same amounts regularly, then on average the 100/0 portfolio will outperform the 90/10 portfolio. Looking at history, the reason to go with anything besides 100/0 over the long term has to do with risk tolerance, not performance.
https://investor.vanguard.com/investor-resources-education/e...