If happiness is the gap between your expectations and what you get, how to keep expectations low without losing the drive of achieving more and being better?
Keep your expectations low by setting achievable goals for yourself.  When you achieve one goal, set another lower goal.   This way, when you reach a goal, it will feel satisfying rather than overwhelming.   Also, always be learning and growing as an individual, this can help keep your expectations low because you never stop improving yourself.