The point of this quote is that life is too short to spend on anger. There is no point in wasting your emotional strength on being angry. Instead, you should just be happy and let bad things sort of slide off your back.
In this quote, the implication is that the person who holds the grudge is the only one who ends up unhappy. The other person does not really care. They are not worried about any grudge so they are able to be happy and "go dancing." The moral of the saying, then, is that it is better to be the person who lets go of things and goes out and has fun. This makes life more satisfying and less stressful.