Joseph's brothers were certainly intelligent enough to make the right judgment about a number of things. If they had lived at a different time, they might have become well educated people or at least successful professional farmers. But no matter how clever a person can be in understanding external things, especially the dead matter, he can be pretty blind to the important things of life, human truths that directly concern him. The ability to judge them correctly is not formed in the same way as e.g. in science or technology; it depends on how we look at them, our point of view (figuratively speaking "where we are") and what values scale we have ​​within.

The brothers sold Joseph when he was 17, and until Jacob's death (i.e. for another ca 30 years) they lived with a burden that weighed heavily on their souls before confessing their guilt to Joseph. And if difficult circumstances had not helped them to travel to Egypt at that time (what a gift they can become for some of us!), they would not have probably done anything on their own to get rid of this yoke...

If a person's heart is not right, he will be basically wrong in his judgments. An adequate level of doubt about ourselves is a necessary condition for a healthy journey through life. After all, the most evil in the world was usually caused by those who did not doubt about themselves at all.