Depression

Non-depressive people don't understand why depressive people don't mind being sad. Of course someone who is used to warmth will pull back from icy water... but someone who lives in the cold and dark reacts differently. They pull in and curl up in a ball. Instead of struggling to get out, they stop moving, and curl up in a ball to conserve their strength. Instead of expending their strength to get out and find help, they curl up and dive deeper. At least down here it isn't frozen.