This is the context:
Suicide has never been dealt with except as a social phenomenon. On the contrary, we are concerned here, at the outset, with the relationship between individual thought and suicide. An act like this is prepared within the silence of the heart, as is a great work of art. The man himself is ignorant of it. One evening he pulls the trigger or jumps. Of an apartment-building manager who had killed himself I was told that he had lost his daughter five years before, that he had changed greatly since, and that experience had "undermined" him. A more exact word cannot be imagined. Beginning to think is beginning to be undermined. Society has but little connection with such beginnings. The worm is in man’s heart. That is where it must be sought. One must follow and understand this fatal game that leads from lucidity in the face of existence to flight from light.
I specifically don't understand why he uses "lead" and what "flight from light" means here.