Why are you still holding onto the cup

Would you waste your time holding up a cup filled with water for no apparent reason? That would be a waste of time and energy.
Yet that is something that we all do, and all the time.

We hold onto our anger, to our disappointment, to our hurt. And we refuse to let go. But at the end of the day, who is the loser?
We, ourselves, because, the other party is happy and away, not hanging on to needless emotions or anger. In fact, most of the time, they do not know, or are not concerned about the fact that you are still hanging onto your anger.

We have everything to lose when we are overly attached to our emotions, to our expectations, to our own world views.
Is there a good enough reason to keep holding onto our anger?

So why are you still holding onto the cup???