The Leg That Remains
The Vishnu Purana describes dharma as a bull standing on four legs in the Satya Yuga, tapas (austerity), shauch (purity), daya (compassion), and satya (truth). Each successive age removes one leg. By the time you reach Kali Yuga, the bull stands on one. That one leg is satya. Truth is what Kali Yuga leaves you when it has stripped everything else away.