The premise that we should always be happy doesn't sit well with me. I think it leads many people to believe that not feeling happy is a bad thing.
I think this kind of thinking leads you to feel emotions on an extreme- either you're happy or you're in some decidedly negative mood. This is not good.
In fact,this is why I found Inside Out so amazing when I watched it- The movie seems to attempt to straight-out state that it's ok to not be happy all the fucking time. In fact,trying to be happy all the time can be poisonous. That's... pretty amazing for a kid's movie, never-mind a movie at all.
Heck, even supposed adult films seem to be stuck in this state of extremes- either things are always going to turn out good or things are always going to be bad, and all the associated emotions with it.
I'd revise the question to ask when you're content, as Dr_Pangloss seems to be implying.
I am quite content with living with a roof over my head with access to a kitchen/fridge and running water and a working sewage system.
That and having entertaining things to read. Fuck the internet- the internet is amazing because it gives me stuff to read.