Your head may help you define what makes you feel a sense of happiness and success, but it is your heart that will confirm it.

If you achieve success at your work, it may not necessarily mean that you are happy. But if you are happy with your work, it generally means that you are also successful. This is because personal happiness has a spillover quality that work success does not.

If your work attitude is "I have to" rather than I "want to" (go into work), then you understand the difference.