A happy life? What is that? I wake up feeling happy some days for no apparent reason and wake up miserable on others for the same.
Happy moments: yes of course and being able to enjoy those.
I'm at my happiest, ie most content, when I know that all my loved ones are happy and preferably surrounded by them.
I agree it's good not to have too high aspirations. Achieve one thing per day is about right and it can be quite a small thing.
I think I was at my most miserable when I was a teenager and life seemed hard, sad and lonely. Then I met my DH and that changed everything for the better.