If ten people like you and ten people dislike you, that doesn’t cancel out. The ten people that don’t like you don’t matter.
Think of it differently – if there are ten people that want to give you a dollar and ten people that don’t, you made ten dollars. You don’t have to turn around and give it to the negative people. You get to keep it.
If a hundred people want to date you and a hundred people don’t, you’re going to have a hundred dates to choose from!
This not only (correctly) informs you not to care about the people who don’t want to buy what you’re selling, it also (correctly) guides you to not waste a single second thinking or talking about the people selling things you don’t want to buy. If you don’t like something, then you can’t much benefit from saying so.
Good and bad don’t cancel out. Bad cancels itself out, and good remains.