There were some things it was better not to know. They caused "metaphysical" anguish, for which there was as yet no remedy. When it was worried, the Tribe was inhibited and unable to act. It was very bad for everyone. The Tribe started to produce toxins that poisoned it. Its long-term survival was more important than short-term knowledge of the truth. If an eye had seen something that the brain knew was dangerous for the rest of the organism, it was better for the brain to put out that eye.