Do you think it's possible to have complete confidence in someone?

Confidence in which aspect? Overall confidence in your ability to handle whatever life throws at you? If that typenof confidence is what you mean, yes it is possible. It is all about who you surround yourself with, your mindset, and continuous cultivator of your own healthy havits and mind set. You can have all the confidence in the world and not realize how unaware you really are, dumb confidence. Which will always lead to a crash and losing confidence. True unwavering, self aware and grounded confidence (aka Hank Hill) is what I would say one should strive to achieve.