General Intelligence:

Why g matters, Linda S. Gottfredson:

"g can be said to be the most powerful single predictor of overall job performance. ... [N]o other measured trait, except perhaps conscientiousness ..., has such general utility across the sweep of jobs in the U.S. economy. More specific personality traits and aptitudes, such as extraversion or spatial aptitude, sometimes seem essential above and beyond g, but across a more limited range of jobs[.]

[N]o other single predictor measured to date (specific aptitude, personality, education, experience) seems to have such consistently high predictive validities for job performance. The clearest exceptions to the predictive superiority of g prove its relative importance. Psychomotor aptitudes sometimes have higher predictive validities than g, but only in low-level work[.] Validities for experience can also sometimes rival those for g, but, once again, they fall as complexity increases[.]"