In life, a first wound is often unavoidable – hurt, grief, disappointment, or physical suffering. But then the mind often fires a second arrow: “This shouldn’t be happening.” “My life is ruined.” The second arrow is the suffering created by resistance, over-thinking and making the pain a story about your life

Suppose they shot a person with an arrow, and then struck him immediately afterward with a second arrow – that person would feel the pain of two arrows.n

So too, when someone without inner training is touched by a painful feeling, they feel two pains, the physical feeling and the mental.

But when someone is more aware, and is touched by a painful feeling, they feel the one pain, physical but not mental.

The Buddha, Samyutta Nikaya, Sallatha Sutta (The Arrow), SN 36.6,