This is a great way to live life by. Though how can you be happy and upset, without one overpowering the other and either leading you to not being satisfied or being passive?
Good question.
Your main disposition should be one of happiness. However this is a certain kind of happiness which really has the sadness included in it so they don't contradict.
This is the happiness of making progress towards a goal. Everyone needs a goal and to work towards it, so you're happy that you're getting closer to your goal, but you're dissatisfied because you still have more to do. This will never lead you to be passive because your whole happiness is in the progress and your sadness in the progress that's yet to be made.
Thought we call it "sadness"... it's not really a sadness either..it's what we call a "bitterness" i.e. a feeling that we still need to do more.
So even this "sadness" leads you directly into more action.
In the Jewish prayers there are times where we focus on the bitterness (like the Tachanun prayer) while most of the day should be happy. I supposes gentiles should also take time out of their day to look at how much more they could be doing.