Intense Training In the Classroom
Before the rookies hit the street, they have to hit the books. They need to know the ins and outs of the job, which requires a lot more mental power than it does physical power. You need to brush up on your critical thinking and problem-solving skills, which are the two most important traits to have.
They also study ethics, behavioral science, report writing, and interrogation techniques. Becoming an FBI agent takes a lot of training, both mentally and physically. This training is so intense that it's used to "weed out" people who aren't really fit for the job.