This is actually the primary focus of a book I just read [1]. The author's primary thesis in this book is that that there are some very interesting reasons why we completely suck at imagining what a future life will be like.
This isn't really a book recommendation - the author took a single idea and chewed it in 20 different ways to make a larger book. However, if this is something you are struggling with right now, you might benefit from it a little.
[1] Stumbling on happiness - https://www.amazon.com/Stumbling-Happiness-Daniel-Gilbert/dp...
[0] http://www.amazon.com/Stumbling-Happiness-Daniel-Gilbert/dp/...
If I agree with the above, I can set aside the quest for ultimate measurement of absolute happiness (e.g. Solon's "Count no man happy until he be dead."[2]) . However, I can still do things that affect relative happiness. When I stopped consulting for boring ERP software, my quality-of-life definitely improved. Again, I won't know if I'm ultimately "happy" until I'm lying on my deathbed. Nevertheless, it feels like I got a little victory from changes like that.
[1]http://www.amazon.com/Stumbling-Happiness-Daniel-Gilbert/dp/...
His book on the topic is here -> http://www.amazon.com/Stumbling-Happiness-Daniel-Gilbert/dp/...
The impatient can look at his TED talk here -> http://www.ted.com/talks/dan_gilbert_asks_why_are_we_happy.h...
This concurs with a lot of other research that suggests that human beings are terrible at estimating what makes them happy. I enjoyed this book on that exact topic: http://www.amazon.com/Stumbling-Happiness-Daniel-Gilbert/dp/...
If you have yet to read it and have any interest in the psychology of happiness (and I can't imagine a sentient human who wouldn't have such an interest), do so post-haste.
https://www.amazon.com/Stumbling-Happiness-Daniel-Gilbert/dp...
https://www.amazon.com/How-Happiness-Approach-Getting-Life/d...