Just because you occasionally act in generous ways, does not mean that you are a generous person. Even entitled and greedy people can spontaneously give when they feel pressured or think it will serve their own interests. In contrast, truly generous people prioritize generosity as a core value and build their live around this commitment. This is manifest in the way they create a giving plan, determine in advance what percentage of their income they give to help others, and then designate that amount to organizations for which they are grateful and that help people they care about.
Why is important? Because the wisdom of the ages, including the teachings of the Bible, tell us that we cannot be happy unless we go beyond random and occasional giving and live a generous life.