Hence personal responsibility is a big factor here. If you just ignore everything and be lazy you're not going to be good for much of anything. Yes there are factors that we can't control but there are many factors that we can control. Pay attention to the right things, and think about what you will need now and in the future and you can maximize your intelligence.
*and this includes adapting one's environment to oneself depending on the circumstances and it's part of being intelligent to notice this.
Now, you can say that people who "ignore significant things" are going to be less intelligent, but let's think. There are kids in the world who have a great intellect - half of them do the responsible things, others don't. Children with disorders of any kind can have the same issues - they do or don't. Honestly, I tend to notice that the more intellectually capable people in this world are more irresponsible, because they can think of how to get away with things; meanwhile, the disordered ones are basically born to say, "Aye aye, sir."