It’s very common to feel like being grateful is difficult when you’re unhappy. However, research shows that simply practicing gratitude (even if you don’t feel like it) may actually make you happier. Give thanks, be grateful and happiness will come with it.
Arthur C Brooks’ article for the New York Times puts it quite eloquently. Choosing actively to be grateful can lead to amazing increases in life satisfaction:
At the time, I believed one should feel grateful in order to give thanks. To do anything else seemed somehow dishonest or fake — a kind of bourgeois, saccharine insincerity that one should reject. It’s best to be emotionally authentic, right? Wrong. Building the best life does not require fealty to feelings in the name of authenticity, but rather rebelling against negative impulses and acting right even when we don’t feel like it. In a nutshell, acting grateful can actually make you grateful.
Beyond rotten circumstances, some people are just naturally more grateful than others. A 2014 article in the journal Social Cognitive and Affective Neuroscience  identified a variation in a gene (CD38) associated with gratitude. Some people simply have a heightened genetic tendency to experience, in the researchers’ words, “global relationship satisfaction, perceived partner responsiveness and positive emotions (particularly love).” That is, those relentlessly positive people you know who seem grateful all the time may simply be mutants.
But we are more than slaves to our feelings, circumstances and genes. Evidence suggests that we can actively choose to practice gratitude — and that doing so raises our happiness.
This is not just self-improvement hokum. For example, researchers in one 2003 study  randomly assigned one group of study participants to keep a short weekly list of the things they were grateful for, while other groups listed hassles or neutral events. Ten weeks later, the first group enjoyed significantly greater life satisfaction than the others. Other studies have shown the same pattern and lead to the same conclusion. If you want a truly happy holiday, choose to keep the “thanks” in Thanksgiving, whether you feel like it or not.