“A regret understood by no one: the regret to be a pessimist. It's not easy to be on the wrong foot with life”

Source: The Picture of Dorian Gray

Last words before being hanged by the British as a spy, (September 22, 1776), according to the account by William Hull based on reports by British Captain John Montresor who was present and who spoke to Hull under a flag of truce the next day:
‘On the morning of his execution,’ continued the officer, ‘my station was near the fatal spot, and I requested the Provost Marshal to permit the prisoner to sit in my marquee, while he was making the necessary preparations. Captain Hale entered: he was calm, and bore himself with gentle dignity, in the consciousness of rectitude and high intentions. He asked for writing materials, which I furnished him: he wrote two letters, one to his mother and one to a brother officer.’ He was shortly after summoned to the gallows. But a few persons were around him, yet his characteristic dying words were remembered. He said, ‘I only regret, that I have but one life to lose for my country.’
Some speculation exists that Hale might have been repeating or paraphrasing lines from Joseph Addison's play Cato, Act IV, Scene IV:
How beautiful is death when earned by virtue.
Who would not be that youth? What pity is it
that we can die but once to serve our country.
See George Dudley Seymour, Captain Nathan Hale, Major John Palsgrave Wyllys, A Digressive History, (1933), p. 39.
Another early variant of his last words exists, as reported in the Independent Chronicle and the Universal Advertiser (17 May 1781):
I am so satisfied with the cause in which I have engaged, that my only regret is, that I have not more lives than one to offer in its service.

Source: Reflections: Life After the White House

Source: Rent

Eighteenth Week.
My Summer in a Garden (1870)