The world is always like this - full of sorrows and happiness. Here everything is abundant. The problem is distribution, not availability.
Indian Philosophy 'Vendanta' says the universe is constructed with single element 'Brahma' and that one manifests to many. If it's true then the only way to happiness is hidden in sorrow somewhere. Kahlil Gibran says :
Your joy is your sorrow unmasked.
And the self, same well from which your laughter rises was oftentimes filled with your tears.
And how else can it be?
The deeper that sorrow carves into your being, the more joy you can contain.
Is not the cup that hold your wine the very cup that was burned in the potter's oven?
And is not the flute that soothes your spirit, the very wood that was hollowed with knives?
When you are joyous, look deep into your heart and you shall find it is only that which has given you sorrow that is giving you joy.
When you are sorrowful look again in your heart, and you shall see that in truth you are weeping for that which has been your delight.
In Indian philosophy, this universe is 'lila by parmatma' (play by God). The reason for its existence is to let us learn and enjoy, to get back to the same spirit where we came from.
By doing our bit to bring happiness into this world, we end up getting rid of our ego. Once we get rid of ego, we may get united with our own soul which is inseparable with GOD.
We have a lot of memories (Sanskar) in our mind which has travelled us since many of previous births and will continue to do so in future births as well. First we learn, then practice, then form a habit, then it becomes our nature which can leave us at the end of our life. But next to that is 'sanskar' which doesn't leave us and keep on travelling with us in future births. That forms our ego, nature and styles in next birth and decides next birth as well.
Each time we learn a lot from environment and build up our ego and decide to contribute a bit in this world. Our ego pushes us to do our bit to leave a mark or contribute towards happiness in this world. But when we get into this process, we find out that ego is the biggest hurdle to happiness. And if we continue to proceed, we can see that our ego is reducing and happiness is increasing in this world.