"I have no spur
To prick the sides of my intent, but only
Vaulting ambition, which o'erleaps itself
And falls on the other."
Vaulting ambition, or ambition that leaps over obstacles, can result in success if the intent is pure. If the motivation is the greater good for the greater number, vaulting ambition can be positive. If the drive to succeed forces and individual to overcome personal weaknesses and become a stronger, more positive individual, then this too can be considered a success. It is when vaulting ambition is used to circumvent events that are meant to occur that it results in destruction. Hamlet's crown was predicted by the hags, and he could have waited for events to take there natural course, but he didn't. He chose vaulting ambition for his own personal gain--not the greater good for the greater number, and this led to his destruction.
He clearly indicates this is a negative "which o'erleaps itself/and falls on the other."
Enotes has some great information available at the following link.