Contracting the Monster Egg and the New Skill
Ban immediately understood everything the moment the System injected it inside his brain. He could have done it the first time but he just wanted to test whether he could understand and memorize them without the System's help.
He knew that he was not a smart or a genius one, he already realized it dozens of times already and he already accepted that fact. He just didn't want to overly rely on the System, he was afraid that his brain might no longer work if he only relied on the System injecting all the knowledge to his brain directly.
And of course, he knew his limit. He was not a stubborn one. If he knew that that's all he can do, then he would immediately ask the System to inject the knowledge, there was no harm to that.