There's a certain subtle ego disorder that creeps up on you slowly when you're used to regularly being introduced as the smartest person someone has met, and you let that slowly become part of your identity. The people I knew who failed out had too big of an ego to seek help, and even were afraid to work too hard, because that made them feel less smart. They didn't outright brag, but were used to others doing their bragging for them, and had a kind of false modesty about them.