It may sound too simple or flowery (and maybe a direct effect of reading a certain book by David Lynch), but I think it often takes a lot of hard work to be happy. Especially when you've been angry for many years, being happy feels like a long, arduous climb. Why? Because it's easy to be ho-hum and annoyed with life when that feels the most familiar. Somehow the happiness you knew when you were younger slowly evaporated as you grew up. Happiness seems fake while sadness and pain feel real. And it can be very difficult to change this.
In my own experience, getting fussed at/dumped upon and feeling abandoned by others all felt real and stable. Happiness seemed to be a fleeting thing and I thought it would always be. The innocence of my childhood had long passed and being an adult somehow meant dealing with a lot of pain and grief. Now all these years later, I find that attitude to be a big illusion.
In a lot of instances, whether we know it or not, we can choose to be happy or not be happy. I've never met an adult who's happy all the time, but I've met my fair share of adults who are sad all the time. Life handed these people lemons and instead of considering the lemonade they could make or learning how to juggle them, they just squash them on their faces and trudge along. And it's a bummer to be around them all the time, at least for me.
There's a difference between venting about life's frustrations and staying stuck in the mud. Venting is like pooping: we all do it and must do it. You find people who vent and get over frustrating matters. You also find people who do nothing but whine and complain. At various over the last few years, I've been in both camps. Frankly, these days, I'd like to stay in the former as much as possible.
When people ask me, "Where do you see yourself in five years?" I say, "being happy." That might not be the best answer to give in a job interview, but I think it's an important attitude to have about life in general. You won't instantly become happy once you start making more money. You won't instantly become happy once you get married. You won't instantly become happy once you have children. You can choose to be happy right now whether or not you're in any of the aforementioned situations.
I don't mean to say all this like I'm a tree-hugger sitting on some grass playing a guitar. All I'm saying is, getting to a state of pure, unashamed happiness requires effort. And it's in my opinion that the effort is worth everything in the long run.