This massively oversells the usefulness of the Kelly Criterion. The opening lines are

> One should buy stock when it is undervalued. What I have always wondered about is how much stock one should buy. A few months ago I stumbled upon the answer which is given by the Kelly criterion.

But the rest of the post analyses a mathematical game which has nothing to do with buying stocks, and is in fact only useful in theoretical situations where you know the precise distribution of outcomes.