Totally agree with RAR pointing out a basic math error here. The probability of positive yearly return being 93% would correspond to return 15% with volatility 10%, not the other way round as stated in the article. 10% return with 15% volatility only gives about a 75% chance of positive yearly return, which is consistent with actual S&P 500 returns since 1966 (36 up years out of 50 = 72%). Besides this point I did enjoy and agree with much of the article.