It happens when something is out of alignment.
It happens when you are out of alignment with the angelic forces that guide you.
You suffer because you or the human system you are in is nit vibrating at a frequency that matches the best potential of the situation and time.
Suffering is pain and to avoid pain, you try to evolve in the right direction.
You try to feel where the painless zone is.
Suffering happens because of the conflict between lights and shadows.
This polarization of pain and pleasure is a reward system designed to keep humankind evolving in the right direction.