Ill-health
Ill-health can make a spiritual man, in that it can break him for the world.
A strong "human rebirth" often comes out of a difficult childhood. The child turns inward, developing the powers of reason and analysis as tools to help him weather a hostile world through understanding. But reason brings its own burden, so he learns to find his joy under the same roof as suffering. As an adult, he fears little.
Suffering and austerities are not necessary to attain enlightenment. However, for some it can help to shape the mind in such a way as to make it more receptive to higher thought. If one has survived the very worst the world has to offer, one becomes fearless. Also, if one suffers much, then one has nothing to lose - in thoughts of dying to the world.