What doesn't kill you makes you stronger / It won't kill you
Used humorously to encourage someone to try something unpleasant or to reassure them that something slightly risky won't do serious harm.
—I don't like this food much. —Eat it, it won't kill you.
What doesn't kill you makes you stronger. You'll see it'll do you good.
—Will it hurt me? —No, what doesn't kill you makes you stronger.