Intelligence is useless if you don't train it, use it, apply it towards something useful, etc.

It's like Michael Phelps who was born with a talent for swimming. But that talent was worthless without putting in endless hours of directed training.

Similarly, a no-talent swimmer can actually learn to swim rather well. And certainly being very successful in life does not require you to be the best swimmer in the world. Just an adequate swimmer will do just fine.