Why does the Buddha always answer a question if asked three times? I've read in many places in the Pali canon that the Buddha will answer a question if asked three times even if the Buddha is extremely reluctant to give the answer. For instance in the Talaputa Sutta the Buddha is asked by Talaputa ,the leader of a troupe of actors, about what will happen to actors when they are reborn. The Buddha clearly doesn't want to say (it's not good news) but Talaputa really pushes it and asks him three times


  "Enough, headman, put that aside. Don't ask me that."
  
  A second time... A third time Talaputa, the head of an acting troupe,
  said: "Lord, I have heard that [...]  What does the Blessed One have
  to say about that?"


The Buddha gives in and delivers the bad news.

But what is the origin of this questioning technique? Why does he always give an answer if pushed like that? Was it a traditional thing in Indian society at that time or was it just a thing with the Buddha? I've only read this in the Pali canon. Does it crop up in other texts and traditions too?
It's fairly clear that three times was a social convention for crossing some sort of line; either that or just a convention of the Buddha. See also DN 3:

‘Reverend Gotama, there are four castes: the Khattiyas, the Brahmins, the merchants and the artisans. And of these four castes three — the Khattiyas, the merchants and the artisans — are entirely subservient to the Brahmins. With regard to this, it is not proper that they should not pay homage to the Brahmins.’ This was the third time Ambattha accused the Sakyans of being menials.
Then the Lord thought: ‘This young man goes too far in abusing the Sakyans.&quot;

and

Again Ambattha remained silent, and the Lord said: ‘Answer me now, Ambattha, this is not a time for silence. Whoever, Ambattha, does not answer a fundamental question put to him by a Tathāgata by the third asking has his head split into seven pieces.’

Walshe, the translator of the above, gives as a note for the second passage, &quot;A curious threat that (as RD observes) never comes to anything, and is of course pre-Buddhist.&quot;
Not sure if the &quot;third time&quot; is also pre-Buddhist, but again, it appears to be some sort of line in the sand for the Buddha at least.