“Forward, the Light Brigade!”
Was there a man dismay’d?
Not tho’ the soldier knew
Some one had blunder’d:
Theirs not to make reply,
Theirs not to reason why,
Theirs but to do and die:
Into the valley of death
Rode the six hundred.

Alfred, Lord Tennyson (1809-1892) English poet

“The Charge of the Light Brigade,” st. 2 (1854)

Popularly, "Ours is not to reason why, ours is but to do or die."