Tl;dr is two much more sane approaches to investing are return driver focused or income generation focused capital allocation instead of asset appreciation and compounding based upon speculative indexing. These btw are what rich people do with their money (hedge funds, managed futures, income generating investments) not park it in index funds and hope the underlyings appreciate due to asset prices going up. Rich people pay 2/20 management fees because the fees pay for true diversification. Diversification is real but requires diversifying return drivers not asset classes. (Asset price changes are just one return driver.) If you are just sitting in asset backed index funds there are a variety of tail events (non-apocalyptic ones) where their action correlation goes to one and you’re perma-in the red until you die.
Low volatility investing is based around the observation that low volatility stocks have higher average returns than high volatility stocks. This article is a good summary: https://www.researchaffiliates.com/en_us/publications/articl...
edit: not sure why the downvotes. if you are interested in a treatment of peer-based utility functions that affect risk premia, see https://www.amazon.com/Missing-Risk-Premium-Volatility-Inves... -- in other words, risk may not be best measured as volatility but instead as the expected relative wealth gain/loss to your market peers. for private employee equity, those peers are other optionholders.