We often don't think of how much we expect after having done something for someone. We tend to attach an expectation to many things we do in a day.
"I cooked dinner and the least you people can do is clear the dishes."
"I worked all day and shouldn't have to do anything at night."
"I helped at the church for years and you'd think I'd get some extra privileges ."
"I won't give you my heart unless you prove your love, because I've been hurt too many times."
You get the picture.
Living/giving/serving from our God-given heart is an unconditional act of love that forgets as soon as possible what good has been done.
Pride demands and insists that "we get what we have coming to us."
After being hurt a lot, we look to protect our heart by being suspicious, jaded, too picky, mean, stubborn, and all for keeping our heart from being more damaged. The main challenge is to trust God with what happens and live from our hearts in a way that we're acting out of love and we're being our true selves with no strings attached.
What do you resent people for? This question will help you discover areas you're not giving from your heart.