This quote means that the more time you spend thinking about something humorous, the more you’ll notice the underlying sadness in the story. It’s sort of like saying that we need to view the world in context- instead of simply looking at a funny story and laughing, if we take the time to consider the entire story and its implications, we can start to see the sadness behind it. This is why it’s important to look at things more carefully, as we may be missing out on something important by simply skimming the surface.