The moment you start to resent somebody you become their slave. They control your dreams, absorb your digestion, rob you of your peace of mind and goodwill, take away the pleasure of your work.
They ruin your spirituality and nullify your prayers. You cannot take a vacation without them going along! They destroy your freedom of mind and hound you wherever you go. There is no way to escape the person you resent.
They are with you when you are awake. They invade your privacy when you sleep. They are close beside you when you eat, when you drive your car, and when you are on the job.
You can never have efficiency or happiness. They influence even the tone of your voice. They require you to take medicine for indigestion, headaches, and loss of energy. They even steal your last moment of consciousness before you go to sleep.
So if you want to be a slave, harbor your resentment.