On one occasion the Blessed One was dwelling at Kosambi in a siṁsapa grove. Then the Blessed One took up a few siṁsapa leaves in his hand and addressed the bhikkhus thus: “What do you think, bhikkhus, which is more numerous: these few siṁsapa leaves that I have taken up in my hand or those in the siṁsapa grove overhead?” sn.v.438
“Venerable sir, the siṁsapa leaves that the Blessed One has taken up in his hand are few, but those in the siṁsapa grove overhead are numerous.”
“So too, bhikkhus, the things I have directly known but have not taught you are numerous, while the things I have taught you are few. And why, bhikkhus, have I not taught those many things? Because they are unbeneficial, irrelevant to the fundamentals of the holy life, and do not lead to revulsion, to dispassion, to cessation, to peace, to direct knowledge, to enlightenment, to Nibbāna. Therefore I have not taught them.
“And what, bhikkhus, have I taught? I have taught: ‘This is suffering’; I have taught: ‘This is the origin of suffering’; I have taught: ‘This is the cessation of suffering’; I have taught: ‘This is the way leading to the cessation of suffering.’ And why, bhikkhus, have I taught this? Because this is beneficial, relevant to the fundamentals of the holy life, and leads to revulsion, to dispassion, to cessation, to peace, to direct knowledge, to enlightenment, to Nibbāna. Therefore I have taught this.
“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.’”