Well... now I am wondering if they had trouble with happiness too.
To be honest, I have strong memories of my parents struggling to make finances work, struggle to accomplish this and that. Struggle to... but not too many times I ever saw them relaxed and happy, and I doubt I ever saw them fully content with their lives. (each for different reasons I won't go into here and mostly for reasons out of their control)
So now I'm asking myself: do I really know how to be happy? More to the point, have I ever really expected to be happy? I expect success. I demand success from myself constantly. But do I know how to find joy in myself, rather than satisfaction in having done the job appropriately?