There is an old saying that you are as happy as you choose to be. While some people have experienced very challenging circumstances and have trouble feeling happy; most miserable people are that way because they let little things get in the way of their happiness.
There are rich, healthy, popular people who feel awful. They might feel like a failure because they are constantly comparing themselves with more successful people (or at least believe all the wonderful posts on social media). They might immerse themselves in negative thoughts about the world and their own immediate surroundings.
But if you are always counting your blessings and trying to serve people who are less fortunate; you might realize that 'It's a Wonderful Life'.