state of mind

What is happiness...just a state of mind..
why can't the state of mind be consistent and be the same all the time then?

One moment you feel so happy, relieved ,accomplished and want to be with the dearones.
Other moment, some or the other thing makes you devastated, disturbed , sad and helpless.
Are all these governed by the karma in the past life? We are not entitled and deserved to have some little happiness last for some time too?
What is life about?
Are all the lives just ruled by the past lives's deeds? Then someone has to be so very pious in the very ever first birth , to be able to enjoy a good life and fotune in all the next coming lives?
If someone is so very pious then they should attain the moksha then itself. They should be liberated. Isn't it?

When people say life is complicated, they correct again saying, it is people who complicate lives. But aren't certain things just way beyond our control?
So if it is indeed beyond control...why is it so? Past life's karma?
How fair is that?