He failed to factor in the controllable variables and didn't correct for many other potentially observable factors.
For example, some people FA and never FO due to a cessation of life-force viability (although one may argue the cessation of life is the ultimate FO). But their actions may allow someone else to observe and FA to a much lower degree while they FO to a significantly greater degree. These observable FA factors may contribute exponentially to a third party enhanced FO.
A wise researcher will always factor in the observable FO analogue in the original FA postulate. Although, admittedly, the FA aspect is frequently intriguing and may overwhelm the full understanding of the FO potential.
FWIW
Crusader Rabbit