The college courses needed for a master's degree, or for a doctorate, are often highly advanced, difficult subjects, and they would be extremely difficult to understand unless a person had already attended the undergraduate courses. The reason the upper-level courses are so difficult, so hard to understand, is that they assume the person already knows, perhaps, 1,000 technical terms learned in earlier college courses. This is similar to having to know the Latin names of all 206 bones in the human body, as just part of those technical terms.