I couldn't disagree much... Happiness can be a darn confusing word for some. The definition of happiness isn't just confined to a particular person, place, or situation. It can have different connotations for different people, but generally it has been seen that happiness comes when we pursue our own things and listen to the voice of our hearts!
When I decided to become a full-time technical writer, I always knew where I was headed for. And from where I stand today, I am extremely proud of it. Happiness stems from belief and confidence in one's own capabilities. The rest, as they say, automatically follows.
Let me assume that you are here because you wanted to be a 'successful' technical writer. Obviously, a lot of thinking must have gone into it. You have certainly made the right decision. First step is always the realization, next is how you work towards achieving your goals and updating your skills. Luckily, this job provides many opportunities to showcase your writing prowess and chances to learn. This reminds me, have you defined a career roadmap for yourself? Start thinking on those lines, if you haven't already. Always remember that you are much more than the business you do, the profit you make, or the users you write for.
Writing well is all about "you." You are as answerable to yourself as you are to the organization you work for. So stop looking for happiness outside, rather make the very best from what little you have. Have no regrets about failures; instead view them as small steps on the climb up to success. At least try it, regardless of whether things work out or not. For me, happiness comes when someone appreciates my work, through the innumerable mails of appreciation and encouragement that I get each month. I wouldn't lie; it's like an obsession. In fact, writing does that to you, and if you still haven't discovered it, maybe your definition of happiness does not matches to mine.