Some thoughts I lately had: "Do I deserve happiness?" Because life seemed unfair to me, not everyone has the same chances in life. Or luck. Some people live poor lifes while others have too much money. Many animals and insects don't have the same life expectancy than humans, others live much longer. There is a lot we can't do anything about. The things a single person can achieve are limited. But how can one be happy in a world, where not everyone is happy?
My answer was: duty. It is my duty to be happy. I owe it to everyone. I mean I eat meat, so I owe it to the animal who died for me. I owe it to the people who don't have the same chances to make the best out of it. If I wouldn't enjoy the things I already have, then there wouldn't be any point in them. It is important to accept that life itself is a coin with two sites. It has the nice and awesome things, but also the cruel things. Sometimes both at once. Is a blue whale evil, because he eats millions of krill a day?
I also think it is okay that the happiness we experience, change over time. I was indeed happy about material things when I was younger. Mainly video games. And christmas presents put a huge smile on my face. But as I grew older, this kind of happiness faded. And I ended up thinking about what happiness really is. And yeah, pretty much came to the same conclusion as you. :)