This is a theoretical and a joke besides, so no one crucify me for this, but:
Imagine despairing of life and wanting to end it, and finding out you could volunteer for a euthanasia program in which all your organs would be donated to people in need. And no one would suffer the trauma of finding your body.
So like, people tend to commit suicide because they feel their life is worthless.
By ensuring their organs will go to others in need, a potential suicide may suddenly find he has a purpose! He will save others!
In finding a purpose, the P-S becomes non-suicidal. But, in becoming non-suicidal, he can no longer find purpose to his life by knowing he is sending his organs on to help others.
Our subject returns to his pit of despondence. And, once there...
...he finds his purpose again.
I know this wouldn't really happen but I was amused by it.