two wrongs don't make a right
Examples
Now, my mom always said two wrongs don't make a right. But she never said anything about four wrongs, and that always left me confused.
My mother always taught me that two wrongs don't make a right. We shouldn't bail out Wall Street. We shouldn't bail out Detroit. It will cost the economy more than the cost of the bailout which is more than the politicians think. We'll run into the hundred of millions to prop these companies up.
But, as my mother used to tell me, two wrongs don't make a right. But I soon figured out that three left turns do.