it is the pace that kills
Doing something at too fast a speed can be dangerous. The phrase originally referred to the hazards of horseback riding. Hey, hey, don't drive so fast—it's the pace that kills!
It is the pace that kills.
Prov. Trying to do too much too fast is bad for you. Nancy: I hate college. Bill: Why? Is the subject material too difficult? Nancy: No, they just expect me to learn too much of it too fast. It is the pace that kills.