We build our bank accounts, we exercise our body, but without happiness, those are meaningless. We have a reservoir of cash in savings, try and maintain health as we get older, but we need to have a pool of happiness inside of us to draw from when things get rough in life. As we grow older, the more we see and endure and suffer with the old age, sickness, and death that surrounds us, it can be a gravitational pull on our mood. So just as we need to keep our body in tune with age through diet and exercise, we need to work hard to practice gratitude daily so we can habitually move towards a happier state. Happiness is very much a skill and a practice, and it's something that we all deserve to have. It's your right to be happy and gratitude for whatever you can feel grateful for is a wonderful avenue in reaching it.
A good way to start is to be grateful to even experience anything at all. Life itself is such an unbelievable and astronomically improbable event that your existence is akin to winning the lottery times infinity. You are the luckiest person ever just to be alive in the first place.
Another way to begin the gratitude process is to imagine you're a caveman who went to sleep and then woke up where you are. It'd be as if you were transported into another dimension or heaven. The society we see would seem magical and wondrous and you feel an overwhelming sensation of awe and gratitude.
The point isn't necessarily to instantly be able to keep that feeling going 24 hours, but keep going back to that feeling. It's a practice that will be an investment in your happiness.