When you struggle against or take a coercive approach with another person, the natural response of that person is to defend their corner and fight back. The same happens inside our own minds. When you are fighting a part of your own mind, that causes the part you are trying to stamp out to dig in, to entrench itself, to defend its corner more vigorously.
Life can be messy for all of us. Sometimes when we try to make improvements, part of our mind panics, and that can hurt.