Camus' interpretation of the Myth of Sisyphus can be applied to human existence and strife. Humans should strive to make the most of an uncomfortable situation. We all push our own rock up the mountain. Some rocks do make it up to the top of the mountain, but most of them roll back down, and then one must start over. There are small struggles humans participate in every day with forces acting against the rock. The happiest one can be is at the top of the mountain, which is why we push the rock up the mountain. It may be that the rock doesn't fall all the way down to the bottom of the mountain, but is a constant difficult struggle.
The only difference is that Sisyphus is immortal, while human struggles are mortal. The struggle is what we make of it; everyone is different. Struggles vary from person to person, but everyone is fighting the same battle. The rock one bears is different from all the other rocks- different weight, shape, etc. There are various inclines which we must climb.
I’m not sure if I would say Sisyphus is happy; it seems to be more of a determination. Sisyphus cannot escape his eternal damnation, so he resolutely resigns himself to sucking it up and carrying it out without whining or complaining. He realizes that this is his life, and continues to push the rock.