Forgiveness is a wonderful thing, we all need it, we all want it and we all need to give it to other people. Whenever we do something to hurt another person we want their forgiveness, Whenever we do something that goes against God, our spirit cries for forgiveness even if we do not realize that is the cause.
We should make asking God for forgiveness a regular part of our day, for all the little mistakes we make we need to ask for forgiveness and help with these things. It is the same for other people. When we hurt another person we need to genuinely apologies for what we have done and ask for their forgiveness. By asking for forgiveness you bring relief to your soul.
So what about when someone does something that upsets you or you think i bad. Forgiving that person is essential to yourself. You see as much as we need forgiveness we also need to forgive, hatred towards another person is a vial poison that eats away at you inside, it causes you to become bitter, resentful and it can ruin any occasion. By choosing to forgive someone you let go of angry feelings towards them, you become lighter on the inside and become free, whereas if you don't it will eat you up and that will ruin your day even more.
And finally Jesus Christ taught that by the way we judge others we too will be judged. (Matthew 7:1-2) And so if we wish to have an enjoyable eternity we need to learn to forgive others. For myself I cant afford not to forgive others with all of the little mistakes I make and it is probably the same for everyone. if you are having a hard time forgiving someone, try doing something nice for that person and help them.