Being Over Prepared, Why is it Considered Negative?

Why is there a negative association with being over prepared?

I remember when I was in school (elementary to college), there was this unspoken rule that the first day of school means not to show up with all your school supplies nor be overly excited about classes. I don't know where that came from but it's easy to see that students know about it. And there is always at least a few students who either don't know or don't care because they show up on the first day with backpacks filled with school supplies, all of their textbooks and showing unbridled desire in wanting to learn. They are looked upon as being over prepared for the first day of class unfortunately with them ending up being labeled as nerds.

But what is so wrong with being over prepared?

I was thinking about the end scene of last week's episode (s6 ep11 "Said the Spider to the Fly") of Teen Wolf where Stiles Stilinski was sitting in his FBI class taking out his school supplies from his messenger bag. He had a contented little smile on his face while he was clicking his pens to make sure they were working as he then proceeded to take out extra pencils. When I look at that scene, I couldn't help comparing him to the other students in the class.

Although the other students were prepared, they made a point of showing that he was over prepared with his binder, index cards in a case and an assortment of writing instruments. He was also the only one interrupting the instructor with questions and not to mention his comical disgusting water outburst. Stiles showed up for his internship enthusiastic and ready to take on his new tasks and assignments. But him being over prepared was used for laughs making it seem like only fools and nerds show up in that way. Again why is being over prepared shown as a bad thing?

There are so many other characters that come to mind that are seen in this way for instance: Steve Urkel (Family Matters), Hermione Granger (Harry Potter) and Paris Geller (Gilmore Girls). These are just a few that I instantly thought of but of course there are many more.

For a real world comparison, I remember during last year's Presidential election, Hillary Clinton was called "over prepared" when she showed up for the debates with actual knowledge instead of spouting ridiculous nonsense. It was seen as a bad thing that she was actually prepared to answer questions and understood the importance of her answers. I didn't understand why being over prepared for a debate was seen as a bad thing. Since the job of being President demands intelligence and the ability to grasp details while being ready to handle any and everything that is associated with the job. I would think being over prepared is something that would be applauded and not used as a negative.

Being smart has always had a somewhat unfavorable quality attached to it but it feels like being over prepared is even worse. But what does that say about our society when those who are considered over prepared are mocked or seen as an outcast?