Humans are still animals, which means survival is one of our strongest, most base instincts. Overcoming that requires an intense and powerful surge of strength and determination.

The kind that most people, but especially a depressed one, simply cannot summon nor maintain for very long. So you just need to wait or speed up burning it out.

Its why depressed people usually aren't the ones killing themselves. Their life is too banal to do anything. Its people who are angry that do it. Someone who finally just snaps from it all, rather than the slow burn of emptiness.