There is a sutta where the Buddha discusses four ways a debate can go between two people: a person could be hard to convince, causing either torment to the speaker but not the listener, torment to the listener but not the speaker etc.. the Buddha makes the final point that it is always worth undertaking the discussion so long as there is a possibility of coming to an understanding, if not, heed mindfulness. What is the reference please?
There are 4 related suttas, but they may not fit your description precisely.
Pañhapuccha Sutta (AN 5.165) describes 5 types of motivations for asking questions:
- Stupidity and bewilderment
- Evil desires and greed
- Desire for knowledge
- 'If, when asked, he answers correctly, well & good. If not, then I will answer correctly [for him].'
The last type of motivation for questioning usually applies to the Buddha and Arahant teachers toward their students.
Pañha Sutta (AN 4.42) describes 4 ways of answering questions:
- There are questions that should be answered categorically [straightforwardly yes, no, this, that].
- There are questions that should be answered with an analytical (qualified) answer [defining or redefining the terms].
- There are questions that should be answered with a counter-question.
- There are questions that should be put aside.
Kathavatthu Sutta (AN 3.67) describes 4 types of persons who are fit and unfit to talk with:
- A person who does not answer a question with the type of answer that is fitting to it (based on AN4.42), is unfit to talk with.
- A person who, in his answer, does not stand by what is possible and impossible, doesn't stand by agreed-upon assumptions, doesn't stand by teachings known to be true, doesn't stand by standard procedure, then he is unfit to talk with.
- A person, when asked a question, wanders from one thing to another, pulls the discussion off the topic, shows anger & aversion and sulks, then he is unfit to talk with.
- A person, when asked a question, puts down [the questioner], crushes him, ridicules him, grasps at his little mistakes, then he is unfit to talk with.
A person who is fit to talk with, is the opposite of the above.
The Buddha concludes the purpose of teaching and discussing, as quoted by Samana Johann in his answer:
For that's the purpose of discussion, that's the purpose of counsel, that's the purpose of drawing near, that's the purpose of lending ear: i.e., the liberation of the mind through no clinging.
The Kesi Sutta (AN 4.111) describes the four approaches the Buddha has towards a student:
- Gentleness or mild training.
- Harshness or harsh training.
- Both gentleness and harshness, or both mild and harsh training.
- Give up teaching the student for whom the 3 methods above do not work.
My person guesses that Ilya Grushevskiy might mix up two Suttas, how ever, here the one in regard of discussion:
"Monks, it's through his way of participating in a discussion that a person can be known as drawing near or not drawing near. One who lends ear draws near; one who doesn't lend ear doesn't draw near. Drawing near, one clearly knows one quality, comprehends one quality, abandons one quality, and realizes one quality. Clearly knowing one quality, comprehending one quality, abandoning one quality, and realizing one quality, one touches right release. For that's the purpose of discussion, that's the purpose of counsel, that's the purpose of drawing near, that's the purpose of lending ear: i.e., the liberation of the mind through no clinging.
Buddha makes the final point that it is always worth undertaking the discussion so long as there is a possibility of coming to an understanding, if not, heed mindfulness."
That part seems to be very far and based on own ideas. My person does not think that such as "always worth undertaking the discussion" would be supportable by dhammic ways of seeing right. See also the Sutta linked, which opposes that right away.
How ever, for one who is attentive, not for one who is inattentive; for one who is discerning, not for one who is not discerning:
"'It's through discussion that a person's discernment may be known, and then only after a long period, not a short period; by one who is attentive, not by one who is inattentive; by one who is discerning, not by one who is not discerning.'
And since this is the way to find out if one is a Noble one or good in its direction, and the Buddha advised not to seek after others for benefit, it's hard to think that he had the view that all discussions are conductive. That in regard of the person. Not to speak about the certain topic. There is a long list of which topics should better not be talked.
How ever, mindfulness on the frames of references is required to do not judge wrong and discriminate probably on preoccupations. So when one is not aware of ones feelings and ones mind state, one would easy and fast become either one who avoidsconductive discussions or gets aversive if involving.
It's then like the OP question here, one mixes up a little bit of this and that, what ever seens tasty for the defilements, e.g. supportive to identify oneself with it.
[Note: This is a gift of Dhamma and not meant for commercial purpose or other low wordily gains by means of trade and exchange.]