Human capital is not just what you know — it is your capacity to apply it under pressure. That capacity rests on executive functions: inhibitory control, working memory, grit, and cognitive flexibility — the machinery that lets you think before acting, hold focus, adapt, and solve problems. In predicting real-world success, executive functions often outperform raw IQ or socioeconomic status.
They are also trainable. Combined cognitive and physical training produces gains that persist for years and beats cognitive training alone,18 and physically fit individuals show measurably stronger executive functions.19 The drains are equally concrete: inadequate sleep, chronic stress, and loneliness all degrade them. The takeaway is unsentimental — if you do not sleep, manage stress, and stay fit, your judgment erodes, and eroded judgment is expensive when it is the thing allocating your capital.