No, they need to understand that the happiness and unhappiness are both very temporary things in life. Life consists of good and bad things, days, etc. A child needs to experience all in order to be the best they can be later in life.
Children should be provided environments in which it is safe for them to try things and fail. This is not to say that you should set things up so that Children fail. It means that if/when they do fail, they are safe from harm. This does not mean that you should protect them from disappointment, just like you shouldn't protect them from achievement. It means that you should be there to help them by discussing what happened and how they can learn from it.
