The reason why we sometimes bear grudges against another person is simply 'expectation'. We expect too much.
When we do things for others, we begin to place expectations on them which they may not even be aware of and when these expectations aren't met, we become angry, bear grudges and keep malice.
Why do we even do things for others with expectation? It is a selfish thing to do, because what it means is that you do not really care about the person but rather you care more about what you are expecting from him/her.
If someone should give you something and then later the person lets you know that because of what he has done for you, you must then do what he wants you to do, how would it feel? Would you feel like this person really cares about you? Answer the question honestly.
This is simply what we do when we make expectations on people because of 'what we have done for them'. It doesn't seem like the right thing to do, because it puts us in a position where we are NOT in control. We depend on the outcome of what we do instead of being free from it therefore more often than not we can become hurt or disappointed when expected outcomes aren't met.
People do not want to be forced or trapped into doing your bidding because of what you've done for them. Who loves that? Do you? Would you like to be chained to fulfil another persons expectation because they've done something for you? That is disguised SLAVERY.
I think a better way to live is to DO THINGS because we really WANT TO DO them. That way, we are free from whatever is the outcome and we derive our joy doing it rather than our happiness being dependent on the result of what we do. What will then really matter and give us genuine satisfaction in life is that deep down in our hearts we are happy that we have done something for another and we enjoyed every moment doing it!
There would be no need to FORCE ourselves or to pretend. We do things because we want to and we enjoy all that we do without expecting anything from anybody. This makes us free from being disappointed. If the person values what we've done, FINE(a bonus). if the person does not, still very FINE(we enjoyed ourselves anyway).
There would be no need to get angry at anyone because you will always be happy. It is no longer your business what people do with whatever you've done for them. It's their business and they're free to do what they like while you remain happy.
In truth, there are responsibilities and actions we have to take, but we must take them up without expectation. We must enjoy doing what we truly want to do without grumbling. You will never get tired of doing good because no matter what people think about your actions or however they choose to value it, IT DOESN'T affect you at all! Our ultimate satisfaction must be derived in the process of doing what we sincerely want to do for others and not giving them the power to determine whether you should be satisfied or not via 'expectation'. Don't FORCE yourself. If you want to really do it, delete expectation. Free yourself and live right. "Love one another" is a universal principle. True Love has NO EXPECTATIONS... you just love and you're happy loving the beloved.
Think about it.