You know, almost every time I read some of your posts two particular quotes by one of my favourite authors come to mind, but I can't find it in English so that I can share it with you, instead I'll give you my own loose translation of them:
You will stumble, but you will not fall, and even if you, by some strange chance do fall, you will not be hurt, and as soon as you manage to get yourself up, you will carry on with your path peacefully. You are different than everything around you, everything threatens you and endangers you, but nothing really bad or beyond repair can't happen to you, because from the very beginning there is an indestructible and hidden spark of life hidden in you, which is more powerful than everything that surrounds you. So, while you are alive, until the very last breath you take, you will suffer for your unnatural position in the world in which you are thrown. It is safe to say that throughout your life there are two things guaranteed - long suffering and sure victory.
One who carries a great, true passion with them, is miserable and tortured more than a hundred other men, but is free from many petty cares and worries that torment most of other men during their lifetime and everyday.
So, to answer your question, I don't really think that we are doomed to be unhappy all our lifetime. I just think that we see ourselves as unhappy compared to others, especially to at first glance carefree SP types. Every person has it's own misery to cope with, and if you manage to find a way to live with it and cope with it you do have a chance for a happy life.