Human beings have many kinds of suffering. Some human beings are put into prisons. Some are destitute. Some are enslaved by others. Thus, they are not actually hell-beings, but their sufferings are like those of hell-beings; they are not actually hungry ghosts, but their sufferings are like those of hungry ghosts; and they are not actually animals, but their sufferings are like those of animals. We think in that way about the sufferings that human beings experience. Some human beings are wealthy and comfortable. However, that wealth and comfort does not last for a very long time. Not being able to enjoy wealth and comfort for a long time, in the end suffering comes to them too. When we think about the suffering that they experience, compassion arises.

The demigods suffer from continual jealousy of and warfare with the gods of the Desire Realm. As for the gods, though comfortable temporarily, later they fall down into painful situations and, at the time of falling, they suffer greatly. Similarly, even the gods of the Form Realm and the Formless Realm cannot just stay there. They fall down to the states of hell-beings, hungry ghosts, animals, humans, and so forth. When they fall, mentally they suffer greatly. Therefore, sentient beings born in the states of the six wanderers have nothing but suffering. If we think about that, compassion can arise.

-- Thrangu Rinpoche