* They do need social interaction: Monkeys live in groups called troops, and they thrive on the company of their own kind. They groom each other, play together, and communicate through a variety of sounds and gestures.
* Isolation can be harmful: While some individuals might be more independent than others, prolonged isolation can lead to stress, anxiety, and even depression in monkeys.
So, the answer is: Monkeys generally don't go "crazy" without another monkey, but they can experience negative effects from social isolation. They need the companionship and interaction of their own species for a healthy and fulfilling life.