A monk called Mālunkyaputta gets fed up. He has been practising for a while and there is a list of questions the Buddha has simply never addressed, and he decides he is done waiting. He goes to him with an ultimatum: answer these, or I am leaving.
I find the whole exchange bracing, because I have been Mālunkyaputta. The demand is entirely reasonable — tell me what you actually think is true about the universe, or why should I trust any of the rest of it — and the answer he gets is not the one he wants.
The questions
There are ten, in pairs and quartets. Is the cosmos eternal, or not eternal? Is it finite, or infinite? Are the soul and the body the same thing, or different things? And, after death, does one who has awakened exist, not exist, both, or neither?
These are not silly questions. They are close to the only questions a certain kind of person wants answered, and every religious system I had encountered before this had confident answers to most of them. That the Buddha does not is the first surprising thing about him.
The arrow
His response is a scenario. Suppose a man has been shot with an arrow thickly smeared with poison, and his friends bring a surgeon. And the man says: wait. I will not have this arrow removed until I know who shot me — his caste, his name, his height, his complexion, which village he is from. Until I know whether the bow was a longbow or a crossbow, what the bowstring was made of, what kind of shaft it was, what feathers it was fletched with, what the arrowhead was.
The detail is the point. It goes on far past where you expect it to stop, and every item is a perfectly sensible thing to want to know. The man is not being stupid. He is being thorough, in a situation where thoroughness is fatal.
The man would die, the Buddha says, and those things would still remain unknown to him.
The reason, which is narrower than people quote
This is where I think the story usually gets flattened. The reason given is not "those questions are meaningless" or "stop thinking so much". It is specific and it is stated as a criterion:
Those positions are undeclared because they are not connected with the goal, not fundamental to the holy life. They do not lead to disenchantment, to dispassion, to cessation, to calming, to direct knowledge, to awakening, to release.
That is a test, and it is a test anyone can apply. Not "is this true" and not "is this interesting" — does knowing this change what happens next. He then says what he has declared, and gives the same reason in the positive: suffering, its origin, its ending, and the way to its ending. Those he teaches because they lead to all the things the ten do not.
So the ten are not thrown out for being unanswerable. They are set aside for being inert. Whatever the answer turns out to be, the arrow is still in you.
Where this is misused
I want to be careful here, because this passage gets deployed badly and I have seen it used to shut down exactly the kind of question the tradition otherwise invites.
It is not an argument against enquiry. The same canon contains long, technical, frequently combative debates — the Buddha argues with materialists, with fatalists, with other teachers, in detail, and does not decline those on the grounds that argument is unspiritual. He set out a test for what to accept that explicitly refuses appeals to authority, including his own. That is not the posture of someone telling people to stop asking.
The refusal is narrow: these ten, on this stated ground. Using it to wave away an inconvenient question about, say, whether a practice works is not applying the teaching. It is borrowing its shape.
Why this was the thing that landed
When I was leaving Christianity, the objection I could never get past was not any particular claim. It was the confidence. A great deal was asserted about matters nobody asking me to believe them could possibly have checked, and the asserting was load-bearing — you were expected to accept the cosmology first, and the practice followed from it.
Here the order is reversed, and the cosmology is largely declined. What is offered is a description of a problem you can verify in your own experience, and a procedure. The metaphysics that would traditionally come first is set aside as not load-bearing — not denied, which is a different move and one he also refuses to make. Just: not the thing in the way.
I do not think that makes it modest. Declining to answer the biggest questions available, on the grounds that answering them would not help, is its own strong claim, and it only holds if the practice does what it says. But it is a claim of a kind I can actually test, which is more than I had.
The bit I keep for work
The arrow has become a working heuristic for me somewhere well outside its intended scope, and I am aware that is slightly ridiculous.
There is a version of debugging where you need to know who wrote this, and why it was done this way, and what they were thinking, and whether the whole approach was wrong — and there is a customer who cannot check out. Both matter. The order matters more, and the appeal of understanding-everything-first is strongest exactly when something is actively bleeding.
Take the arrow out. The archer's name will still be there afterwards, and by then you will be able to think about it clearly.