Being happy is all about perspective. Yes you can choose happiness. Happiness is a choice.
So why are some people just not happy? Well once reason is as a world we have a tendency to focus on the things we don’t have. Instead we should be grateful for the things we do have. Remember everything good in your life comes from God (James 1:17). So it
God has a different will for all of us so its up to Him how and when He blesses us. Again happiness comes down to perspective. Once you change your perspective you will see how blessed you really are.
Finally remember it’s always best to be humble. God resists the proud and gives grace to the humble.