Why were cadet IQs not a correlation indicator for completion of beast

Because grit (which comprises of a person's perseverance and passion) is a more significant indicator and predictor of success rather than the conventional "whole candidate score"

Explanation:

In the book, Grit: The Power of Passion and Perseverance by Angela Duckworth, she undertook a study of 1,200 new cadets (who were in their first year) about to start "Beast Barracks," an intense seven weeks training program in which the cadets were drilled 17 hours nonstop on a daily basis. In her research, Angela argued that grit (which comprises of a person's perseverance and passion) is amongst the most vital indicator and predictor of success rather than the conventional assessment employed by the cadet school tagged "whole candidate score" (which is a weighted measure of a student's SATs, high school ranking, leadership ability, and physical fitness). Her thesis have since been seen to be a true correlation indicator for completion of beast.