He's such a rock of confidence on the surface. He knows he has to appear that way. Whether he's maneuvering against a deceptive Romulan, standing up to a tough-talking Klingon, or even negotiating with a wily Ferengi, no one could doubt the iron will that fuels Jean-Luc Picard's being... at least, when you look at him.
We've seen him at his lowest, too, though. Not to make this a Kirk-versus-Picard thing, but with Kirk, even in his vulnerable moments, he still had an air of stoicism, as if even in private, he felt it was unseemly somehow to let go, to unclench, to release his anguish.
I would argue Picard's vulnerabilities define him as much as his strengths: tearfully admitting to his brother Robert his shame at being unable to overcome the Borg; struggling to resist Gul Madred's attempts to brainwash him (and almost failing); taking his rage and thirst for revenge against the Borg out on Lily Sloane.
They were all shocking moments, but I think we needed to see them in order to help uncover who Picard is as a person. He is an altruistic, noble, principled man, no doubt, but he also has a potential for arrogance and overconfidence that rivals Q. And credit where credit's due: Patrick Stewart sold the role, folks. We have been extremely fortunate to have had him as an actor.
The difference between Picard and Q, though, is that Picard has learned to keep his arrogance in check. He rises above his baser instincts to walk the straight and narrow path. He knows he must, because his crew needs him to: whether it means taking command of the Stargazer in a crisis situation, or defying a Starfleet admiral and leading his Enterprise crew to rescue a people from forced relocation. The better angels of his nature win out in the end because they must. That makes Picard a great captain and a more complete character as well.
Chris Pine's Kirk