AbstractThe existence of free will and its prerequisites have entertained countless debates. The position one takes in these debates dictates their outlook on limitations of predicting human psychology. Sam Harris (2012), in his book, misses out on exploring these consequences accepting or rejecting free will has for the predictability of human decision‐making and action‐taking. Likewise, referencers of his work addressed this topic only peripherally and, to the best of my knowledge, have never explored its consequences in depth. Therefore, in the present review, I aim to demonstrate and formalize the following: If we understand human cognition and behavior as the result of environmental and individual causes that both are knowable, adding a per definition indeterminable source, namely, free will, can only reduce the maximum possible power of any used prediction model. Accepting a free human will renders error‐free foresight theoretically, and empirically, impossible. This has consequences for all forecasting and planning methods that concern human agents as well as their tools’ utility (e.g., scenarios and psychological analysis). I address the consequences free will belief has conceptually for three application fields: management and leadership, historic analysis, and theory building.