Why is it hard for people to be happy?

Why is it hard for people to be happy?

A question that some of us regularly think.  Why is it so hard to accept the good things we have in our lives? Maybe cause we're always wanting more, and it's not bad; we want good things to happen to us, but sometimes expecting too much from others or even of oneself can lead you to a constant disappointment. Ok, this is looking pretty depressing.
What I'm trying to say it's that maybe we should only worry of being nice with others; not all the time cause it's impossible to always be in a good mood when you're kind of blue... but if we tried to cheer someone up instead of getting them down  it'd be easier. If we started from doing the things we like, the simple things that make us feel good, like chatting with a friend, going out alone or with someone to a new place, watching your favorite shows, listening the music you like... that kind of things; everyone would be more cheerful, we would regret less things.
We should take a moment to think: what are the things that make me happy? and start doing some of them everyday. Do something nice for you and someone else.