Many people are too high strung.
I understand that life is tiring, hard, and strenuous to us at times. I've had my fair share of those days. But I'm usually able to bounce back. I think more people should be able to move on from the frustrations and wrongs that befall them.
Close friends and family often tell me that I am too laid back or should be mad or upset at something I'm not. They'll tell me it's okay to feel upset or mad because of X,Y,Z and I'll sit there and listen. Agree to some points that I should be mad at; but overall feel no different about the situation. It's not that I don't appreciate the advice and ideas brought to my attention, but it's more that I've accepted the feelings and realize being mad serves no purpose other than wasting time.
Think about it, there are people in the world that have been known to hold grudges from past angers fears, or sadness. As such minutes, hours, months, and years are wasted which to be used on much better things. Relationships with that person could become stronger if there's some understanding and forgiveness to those that make us upset. Goals could be better pursued if there's no fear of what others may think. Happiness could be attained faster if there's no pain to cause or sustain.
All the time I would have been upset or mad I've been able to be constructive and have a more productive life. I've been able to do much more because I didn't feel like something was holding me back. I feel more at peace than I would had I chosen to sit and pout over something that could be easily forgiven or brushed off your shoulder.
I don't find pleasure in holding a grudge and it prevents me from enjoying the little things. Going to get ice cream with a friend. Trying something I like to do. These are some of the things I get to do because I don't hold grudges. If everyone held a grudge the world would become very lonely. People are not perfect and I know this because I make people upset as well. If we can all forgive and make things go smoother, there'd be a lot less friction to deal with.
So take some time in the present. Make it so you can enjoy everything life throws at you. I know it won't be easy but we have a hand in how easy it can be for us. Don't close doors because of a simple grudge. Use forgiveness, understanding, and courage, to do more than you can ever think. That will help you on your path to happiness.