Fighting?

“I learned long ago, never to wrestle with a pig, you get dirty; and besides, the pig likes it.”
-- George Bernard Shaw

“You must not fight too often with one enemy, or you will teach him all your art of war.”
-- Napoleon Bonaparte

“The painful warrior famous for fight, After a thousand victories, once foil'd, Is from the books of honor razed quite, And all the rest forgot for which he toil'd”
-- William Shakespeare