Elsewhere in the book, Steve Horwitz writes this: "The same dark forces of time and ignorance that plague market processes and, for Keynes, implied the need for discretionary economic policy, also haunt the policy-implementation process." (p. 208).
This is an unusual way of putting it! When Keynes cited the "dark forces of time and ignorance", he was actually talking about the social object of skilled investment. This was something that entrepreneurs did - the most important thing they did for the society at large - and not something that required discretionary economic policy. Keynes notes that some investors contribute more to this end than others, and that the tendency toward liquidity preference is one example of satisfying private ends to the detriment of social ends (that's the old fallacy of composition point that economists have been pressing since at least Adam Smith and Mandeville). So there are tensions in the behavior of entrerpreneurs, but this was not an area where public policy was invoked at all!