What does it mean to be serious?

Have you ever thought what it means to be serious? Is it the stopping of laughter? To have a smile on your face, would that indicate that you are not serious? To want to look at a tree and see the beauty of a tree, would that be lack of seriousness? To want to know why people look that way, what they wear, why they talk that way, would that be lack of seriousness? Or would seriousness be always having a long face, always saying: "Am I doing the right thing, am I conforming to a pattern"?
- J. Krishnamurti