In the passage below from the Dukkha Sutta, the Buddha's disciple Sariputta provides insight into the First Noble Truth through a categorization of three kinds of suffering (dukkha: anguish, distress) experienced by sentient beings on the Wheel of Existence. This is what Je Tsongkhapa means In Verse 8 of The Three Principal Aspects of the Path when he says that all sentient beings are "endlessly tortured by the three sufferings":

1. The suffering of pain: birth, aging, sickness, death, physical injury: all are painful.
2. The suffering of change: friends become enemies and vice versa; what was once perceived as pleasant becomes painful; once we get what we want, it turns out not to be enough: all are painful.
3. Pervasive suffering: as long as the five skandhas (form, sensation, perception, mental habits, consciousness) remain contaminated by the Three Poisons, the resulting mental phenomena ("fabrications") will inevitably be painful.