Happiness is not enough to insure a fulfilling life. It is imperative to have courage, not merely happiness. To be fulfilling, happiness must derive from the courage that leads one to face stressful circumstances and to do the necessary hard work of transforming them from potential disasters into growth opportunities.
One particularly relevant study by my research team and me showed that hardiness was more effective than optimism (happiness) in helping people cope with stresses by growing through them, rather than stagnating. This showed how happiness, devoid of courage, can be laced with naive complacency.