There's nothing wrong in experiencing those "negative" emotions like sadness, anger, jealousy etc. The important thing is to know what you're feeling and get through it. There are all too often outbursts of above mentioned emotions, because people tend to bubble it up and then one little happens and the bubble bursts. That is the problem. I think people should be more expressive and share the emotions in a constructive way. For example "I am angry that a certain action lead to me not reaching a certain goal". Recognize the emotion, address it, learn from it and hopefully move on.