“Bhikkhus, just as a stick thrown up into the air falls now on its bottom, now on its top, so too as beings roam and wander on, hindered by ignorance and fettered by craving, now they go from this world to the other world, now they come from the other world to this world. For what reason? Because they have not seen the Four Noble Truths. What four? The noble truth of suffering … the noble truth of the way leading to the cessation of suffering. sn.v.440
“Therefore, bhikkhus, an exertion should be made to understand: ‘This is suffering.’… An exertion should be made to understand: ‘This is the way leading to the cessation of suffering.’”