Grievious
Srimad-Bhagavatam
SB Canto 3
SB 3.12.33, Purport:
The best way to compensate for one's sinful acts is to give up one's body at once, and Brahmā, the leader of the living entities, showed this by his personal example. Brahmā has a fabulous duration of life, but he was obliged to give up his body due to his grievous sin, even though he had merely contemplated it in his mind without having actually done it.
This is a lesson for the living entities, showing how sinful an act it is to indulge in unrestricted sex life. Even to think of abominable sex life is sinful, and to compensate for such acts, one has to give up his body. In other words, one's duration of life, blessings, opulence, etc., are decreased by sinful acts, and the most dangerous type of sinful act is unrestricted sex.