Sadness and Happiness

When we tell a story, certain scenes are inherently happy (like the sun rising on a beautiful new day) and others inherently sad (like rain pouring down at a funeral). Some of them are simple enough, probably because they tug at the core principles of humanity (e.g. death is sad).

But any of these scenes can be turned around in a number of ways. A funeral could be a happy scene if the person who died was a murderous despot. A rising sun could be depressing if it illuminated a village that had been burned to the ground the night before.

Similarly, scenes can be changed between happy and sad because of the people in that scene. A funeral can be a happy thing if a person attending it met the woman of his dreams there. However, by adding people to a scene, we can sometimes muddle the message. When a hero sacrifices himself to defeat the villain, his funeral will be sad, but we will also be happy that the hero was successful.

Audiences are the same way: they're people. They have their own thoughts, feelings, and emotions. When they read your work, you may have a scene that is happiness in its purest form, but they may feel sorrow. This is not necessarily due to any aspect of your writing. It may just mean that you have affected them emotionally, though not toward a specific emotion. It could also mean that they just have a lot on their mind and it is influencing their judgement. In any case, realize that happiness and sadness can be a result of several different factors working together or one factor being stronger than all the others (or the audience dealing with their own things). It is very rare that an emotion is pure and simple.