The journey is all of your life. I believe you should aim for an enjoyable journey [of life], not to be confused with short term journeys and destinations. In

The journey is all of your life. I believe you should aim for an enjoyable journey [of life], not to be confused with short term journeys and destinations. In your example, if studying and acing your exam gives you more happiness in the long run (despite less happiness in the short term), it's worth it to suffer a bit now and study. If acing your exam doesn't give you more happiness in the long run, then compare it against the happiness you get if you don't ace it, and make a decision.