There will always be things in life that are beyond our control. If we tie our happiness to specific circumstances and rigid outcomes then whatever we can't control becomes a source of stress and other unpleasant emotions.
Famous inspirational quote greeting card, featuring the quote, "peace. it does not mean to be in a place where there is no noise, trouble or hard work. it means to be in the midst of those things and still be calm in your heart.", from Quotable Cards.