It is difficult to say that iq tests predict career success in a definitive way because

You cannot measure the physical skill of a worker based entirely off of mental acuity. There's also the fact that, in the workplace, it's always a matter of who you know, not what you know. There will sometimes be a certain degree of favoritism that predicts career success.

Complementary goods. they go together, thats why one price increase and the others demand increases