There's this part in Harry Potter and the Half Blood Prince where Harry is suddenly the best at Potions and Hermione gets pissed at him rather than being happy that he's doing well. The same thing happens in How To Train Your Dragon when Hiccup is suddenly way better than Astrid in class and she also gets super annoyed.
When I read that part in Harry Potter for the first time, I completely agreed with how Hermione was thinking. I used to be the one that got the highest in my own class, so if someone was suddenly getting better grades, it would piss me off too. But why? Well, it's simple. We don't understand WHY. Why is it that this person is suddenly the best? What's their trick? Because there must be a trick. Hermione and Astrid knows what it takes to be the best and have consistently acted upon their abilities, thereby making them the best. When someone else gets ahead, they want to know how. And when that person says they're doing exactly what they used to do, the logic doesn't sit right and nothing makes sense. The inability to make sense of it all is what pisses them off. IF they had seen Harry or Hiccup improve with hard work and practice, they would be happy for the boys. But that wasn't the case.
In Harry's case, he had a book that told him better instructions for potions. In Hiccup's case, he studied a dragon's behaviour to better understand how they reacted to things. Once Hermione and Astrid figure out how the heck these boys had suddenly surpassed them, they were calmer. It wasn't that Harry had suddenly become smarter than Hermione (I mean let's face it, that's impossible) or that Hiccup was suddenly stronger than Astrid (like yeah right, totally) it was that they were doing things from a different angle. Now that the world made sense again, they could stop getting frustrated and move on with their lives.
I must say though, I think Harry's example was more like he was cheating... At least Hiccup studied the dragon and figured things out for himself. Harry just copied the Prince's notes...