Let me put it this way: one of the leads of this book has been on a journey for a good long while, and this is a big milestone in their life. Knowing something of where they've been along the way to this point, and the work they've put into self-improvement, there's a lot emotionally invested.
It's a triumph of sorts, for all that it could still go horrifically awry...or straight to further glory.
Call them celebratory tears. At least for now.