"The Bible talks plentifully about joy, but it nowhere talks about a 'happy Christian.' Happiness depends on what happens; joy does not. Remember, Jesus Christ had joy, and He prays 'that they might have MY joy fulfilled in themselves.'"
- Oswald Chambers-
Happiness, what an ambiguous word! If you asked 100 different people the definition of happiness, you would get 100 different definitions. A couple months ago I was eating lunch with my father when he asked me if I was happy. I thought about the question for a moment and answered that I wasn't sure if I was happy, but I knew that I was content. To me, happiness is directly connected with life circumstances (what “happens”); those conditions beyond our control. The tapestry of life we weave directly affects our temporal happiness. At that moment with my father I couldn't say that my "life circumstances" were at the "happy" point. Happiness is fickle, it changes as we change. Fortunately, life circumstances do change. If we are at a point where happiness seems elusive, our situation could change and bring us into a happier state.
Contentment, on the other hand, is measured by the ability to rest in our circumstances knowing that we can overcome the difficulties of life and maintain a sense of self though it all. Happiness may not be attainable due to life situations at a particular time, but contentment is always within our grasp. Choosing to be content is within our control alone. The desire to live life, no matter the circumstances, with an attitude of fulfillment paves the road of contentment. For those fortunate enough to experience happiness from life circumstances coupled with contentment from a settled state of mind are then able to experience the final step - true joy.
This I know for sure.