1. Why don't the origins or the nature of the poisoned arrow matter? Is this analogous to not knowing the nature or purpose of the world?
2. Are there some metaphysical truths that are important to know, and others that are useless speculation? How can this be determined?
3. What does it mean for something to be useful?
4. Presumably there are many different Dharmas, or ways of living, how can we know which to follow without getting involved in metaphysical discussions?
"He [Buddha] used the following parable to illustrate the attitude of those who cannot distinguish between what is useful and what is not:
'Suppose someone was hit by a poisoned arrow and his friends and relatives found a doctor able to remove the arrow. If this man were to say, 'I will not have this arrow taken out until I know whether the person who had shot it was a priest, a prince or a merchant, his name and his family. I will not have it taken out until I know what kind of bow was used and whether the arrowhead was an ordinary one or an iron one.' That person would die before all these things are ever known to him.'
In the same way, those who say they will not practice the Dharma until they know whether the world is eternal or not, infinite or not, will die before these questions are ever answered."
Thích Nhất Hạnh gives a similar version:
The Buddha always told his disciples not to waste their time and energy in metaphysical speculation. Whenever he was asked a metaphysical question, he remained silent. Instead, he directed his disciples toward practical efforts. Questioned one day about the problem of the infinity of the world, the Buddha said, "Whether the world is finite or infinite, limited or unlimited, the problem of your liberation remains the same." Another time he said, "Suppose a man is struck by a poisoned arrow and the doctor wishes to take out the arrow immediately. Suppose the man does not want the arrow removed until he knows who shot it, his age, his parents, and why he shot it. What would happen? If he were to wait until all these questions have been answered, the man might die first." Life is so short. It must not be spent in endless metaphysical speculation that does not bring us any closer to the truth.
Nhất Hạnh, Thích; Kapleau, Philip (2005). Zen Keys. Three Leaves Press. p. 42.