Compassionate Understanding. From what I remember of the Buddha's story, understanding came first, Right View came first. He opened to Dukkha, understood that he was also subject to these things and compassion arose. So I believe understanding is the fuel that begins the process, and compassion is very close afterwards. Compassion is the power and the strength and the intention that is very strong and very big. Thus in that way, it will fuel the other Paramis.
It's helpful to think of Compassionate Understanding as being Right View and Right Intention. Those two factors of the Eightfold Path fuel all beneficial actions, speech and thoughts. Compassion and wisdom.