The distinction lies in the difference between being confident and acting confident.
You can act confident without being confident but if you are confident you will be confident.
Hm? Though I am confident about a choice few of my political beliefs I don't often act as such, and experience tells me it is also not received that way.
I don't think that's it. He says he tends to arrive at right answers after long and careful thought while people around him jump into conclusions and force them forward.
There's no magic bullet for confidence. You can try faking it till you make it. Ultimately good work will lead to confidence. If a bunch of boisterous sales guys were constantly "alphaing" me with erroneous solutions and I knew with some thought I could come up with something better I know I would start to gain confidence through that process.