Consider this: You've always loved geology, you scored high on all of your college geology exams and you landed a great job as a junior geologist after graduating. And much to your surprise, you didn't like it at all.
Although that doesn't happen to every college graduate, it does occur often, because in many ways we're making the decision to pursue a career in the abstract with only a few classes and tests to inform us. In reality, there's often a difference between what it's like to study something and what it's like to actually do something. One way to prevent this issue is to work as an intern.