I am superbly lucky. I was born into privilege to such an extent that I have never needed to worry about financial security, my personal safety, or anything really. So much so that I had no idea that these were things to be worried about for many years. Everything I have ever needed has been handed on a silver platter to me and I have done absolutely nothing to earn this. In terms of leg ups I can say I was pushed skywards by Hercules himself. I was lucky to have grown up in Malaysia, which isn't perfect but it has nearly no natural disasters (landslides being one of the worse things we have) and its free of widespread violence. This is especially salient right now as people risk their lives just to cross the sea to come here, so that they can live their lives free of violence and persecution. I am totally grateful for all of it. I realize that this leg up has made it so much easier to achieve great things. It has given me a childhood free of worry or fear. And being a totally useless man, I managed to have the best partner a person could ask for fall on my lap. Heck, if I were struck by a falling plane right now, I would still consider myself on the whole as still pretty lucky in terms of the life I've been given.
Your life might not be as privileged, but trust me you are lucky too. You are reading this on a computer, have electricity to power it and literacy in English to understand me (which really helps you out anywhere you go on this planet). We are both among the richest people that have lived considering that for most of human history the vast majority of people were dirt poor and even among the 7 billion people around today, you are in the top few percent. While you could probably list out a myriad of reasons why "my life sucks!" Know that you can list out ten times more reasons to be grateful.
Lets begin with being alive. To exist and to be consciously aware of it involves miracle level luck. I will let this guy explain it since he explains it best: https://www.youtube.com/watch?v=3D7bsf5toMw
If you still don't see the odds involved this spells it out further : http://www.iflscience.com/plants-and-animals/what-are-odds-you-becoming-exactly-you
TLDR of the two above links - you should not exist. In terms of odds, you existing is the inverse of infinity. It is so small that even in the vast universe out there, till the end of time, there will be only one instance of you. No encores. A dice rolling 6 every second for a whole year is more likely.
Why am I seemingly trying to force you to admit that you are one lucky son of a gun? Because it makes you happier. It really does. When I feel down even after the shittiest day, I just think to how much I have and my goodness do I realize I have so much to be happy about. Heck, from some perspectives (like my girlfriend's) even the crappy stuff is a privilege to behold, as it will never happen again and you and only you get to witness it from your perspective. Some reading this might have a lot less reasons than I do to feel grateful for, especially if you are somehow reading this from a rickety overloaded boat that's about to sink, but you should still hold to the emotion of gratitude because in the end happiness is not about your circumstance and what you have.
Even if you have everything, without gratitude, you will be miserable. No matter how little you have, if you are able to appreciate it, you can be happy. I hope my little rant above has given you a little perspective and will allow you to appreciate what you have a little better so that you can be happier.