The story is that there was a cobra who was practising loving-kindness meditation in a forest all by herself, and then an old woman came along and the old woman mistook the cobra for a rope. So as was practising loving-kindness, she allowed the woman to use her as a rope for the firewood she had collected. The old woman went home and this cobra escaped with lots of difficulties, lots of pain, lots of wounds, and so on.
She went to the meditation teacher and told the meditation teacher: See what happened. I was practising loving-kindness. I’m suffering as a result of the loving-kindness. And the teacher said: You have been practising idiotic compassion, not loving-kindness. You have to learn to hiss sometimes.
So sometimes we need to hiss, to assert ourselves, to be firm. But again be clear while you are being firm that your motive, what is inside, is really compassion. So the point I’m making is, loving-kindness doesn’t mean that you are always passive, allowing others to exploit you. With wisdom you should know when to assert yourself and when to be gentle.