I think being sad has a lot to do with the way you see life. Therefore my theory is you can make yourself sad. Not that being sad is a bad thing, we need to be sad sometimes. But anyway, this is how I came upon this. Yesterday (i think it was yesterday) I had remembered something that made me sort of sad and I was going to write about it later, but today, I've forgotten what it was. All I remember is feeling somewhat sad yesterday over something, but since I've forgotten it I'm happy right now :) And that's even better! I sat here and tried to remember it when it dawned on me: why sit here and try to remember something sad, if you've forgotten about it, don't try to remember it. Stay with the happy feeling.