I love this it's a very wise philosophy. As much as possible I try not to perpetuate my own (at times very pervasive) misery and I encourage my friends to adopt the same mindset expressed in that quote. We exercise a lot more control over our happiness than we realise. It's often about capitalising on life's opportunities and investing in activities/occupations that will fuel our contentment. Of course, when you're mired in an all-consuming depression it's exceedingly - even impossibly - hard to think of any activity that could make you happy.