Fwiw, Mumtooneboy, I know several mums who are very self-confident as you describe; one runs her own communications company, one is a head-teacher and one is a senior accountant. They all have at least one teen who have issues, just the same as those of us who are second guessing ourselves all the time.
A bit of parental self-doubt is no bad thing I think as it makes you question and review your actions. You haven't failed. He just needs to make his own mistakes in his own time. And it is exhausting to witness. 
McMen I agree with Staywithmemyblood you sound so caring and put so much energy in to your parenting, and it sounds as if you are getting scant appreciation for your efforts at the moment. Even when you are arguing though, it will filter through to your DD that you care and that will make all the difference in the long run.
Lovely post Peebles and so good to hear. Great that you and your DD have come out stronger on the other side!
. Also really brilliant that she has found her "thing"!
Love the forest analogy Staywithmemyblood!
Things are very up and down here ATM.
"When she's good, she's very very good
And when she's bad, she's horrid!"
Is that Hillaire Belloc? Can't remember!