M.M.
I think you've asked one of those questions that has no "do it this way" answer -- much like how to you know if you're child is really trying in school or it's over his head?
I have a 26 year old child who has had his ups and downs, as have most children. At 13 -- his impolosion year -- I don't think I could have given him away. I also raised a child knowing that there would be a time he'd go out on his own, and he'd was responsible for his own actions. I did not bail him out of all of his mistakes, I did not try to entertain him every second of every day (I wanted him to be happy without the continual entertainment of "stuff"), I did not intercede in his fights (unless I thought it was ABSOLUTELY necessary). I told him I was behind him, would stand next to him, but I wouldn't stand in front of him to allow him to misuse people's feelings or his own.
I think some of the adults of today are irresponsible and selfish. I think some parents, in their attempts to help their children, did not show their children how to get along with people, how to survive well, were too eager to always find fault with the other person. (PLease don't think I didn't go to bat for this child when I thought something was wrong -- but beleive me, not every teacher is wrong all the time, the coach is not wrong all the time, etc.)
We smelled the flowers, we spent time together, we talked, we played, we "studied" together. He did not have a television in his room -- why do we feel our children are not part of a family?
I think childen become happy adults because they're happy children. I think children become happy because they've learned to fit well into their relationships, know their parents love them, they have a purpose in life (Yes, I did think, at times, Tony's purpose was to make sure I lost my mind, patience, temper.....).
I'll leave you with two things:
In fifth grade, my son said to me, "You're destroying my self-esteem."
I looked at him, and told him, "Let's get real! In real life, you don't get to do make-overs, take tests again because you failed them. In real life, Tony, you'll be fired for not completing a project on time, for treating people like you're treating your friends. School is to help you learn stuff you'll need when you become an adult. You'll find your self esteem comes from knowing you did a job well and not because you were handed it."
Secondly, my wise mother told me, "You're allowed to have a personality conflict with one or two people, but if you're having a personality conflict with everyone, then it's you!"
Good luck. The fact you're asking how to make a child a happy adult says to me you're on the right path. Parenting is hard darn work!
My son is now a well-liked, wonderful young adult. He doesn't do everything I think he should and some of his decisions are not ones I would have made. But just because it's not mine doesn't mean it's wrong. Seems to be happy ...