I don't know that I thought in terms of confidence.
Around 2 years ago, after I'd been dealing for a year with the idea that maybe I really was trans, the little voice I call my "inner oracle" told me, "you're going to transition. Just thought you'd like to know." I've learned over my life that that voice, and in general the part of "me" that isn't my conscious self, is a lot wiser and smarter than I (conscious self) am, so I might as well go along with what it tells me.
I've been doing it step by step, first getting to know other trans people, then just thinking about myself differently and talking to a few people I trust, and then finally started coming out to whole communities in March 2016.
It helped that I'd been doing gender-nonconformity for maybe 10 years before I even started thinking I might really be trans.
Oh, and HappyMoni is spot-on.