You will spend the next 50 years doing more things and reflecting on all of those things that you did in your first 50 years.
Toward the end of those 100 years of fruitful living you will spend a good deal of time continuing to reflect and evaluating those 100 years of life.
So, make sure you spend time doing things that are worth reflecting on and that bring value to you and to others.
It is in so doing you will find happiness in a life that was truly worth living.