Every man for his own hand, as Henry Wynd fought. Every man for
himself; every man seeks his own advantage. When the feud between Clan
Chattan and Clan Kay was decided by deadly combat on the North Inch of
Perth, one of the men of Clan Chattan deserted, and Henry Wynd, a
bandy-legged smith, volunteered for half-a-crown to supply his place.
After killing one man he relaxed in his efforts, and on being asked
why, replied, “I have done enough for half-a-crown.” He
was promised wages according to his deserts, and fought bravely. After
the battle he was asked what he fought for, and gave for answer that
he fought “for his own hand;” whence the proverb.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894