So when I talk to somebody and they have a problem, I try to fix it. But a lot of my friends in the past have to deal with their own insecurities, and it's actually become something of a pet peeve of mine. I hate when people talk about how they messed up an interview, or how they look awful today, or they'll never be successful, or anything like that. I can't stand hearing something complain about things like that because I am absolutely powerless in that situation. If there is a way to convince somebody that the lies they are being told are the lies circling around in their own head, I don't know of it. I can help with homework all day. Heck if I don't understand the material I can go look it up and teach it to them. But you can't help somebody with insecurity.
I can actively reassure a friend that he's a good actor, or that she looks good, but to my knowledge people don't process conflicting information of that nature in the right way. They think that you're just lying to be a good friend, or that your opinion isn't the one that matters on this issue (for example, they'll say or think something like "I know you like this piece, but you're not a publisher so what your opinion doesn't hold any weight). It's frustrating because there isn't any way to counter such an argument that they will seriously consider.
That's the important thing here. When people are insecure about themselves, it means that they have a voice in their head that they value over the voices of those around them. It's not hard to understand why, considering the origin. If that voice is in your own head, it must be you that thinks that way, right? Wrong. I think friends and family are generally more likely to provide an accurate depiction of who you are and how well you're doing simply because they're on the outside looking in. "Sure," you may tell yourself. "They may think I handled myself well during that interview, but X family member doesn't know that I forgot to brush my teeth today!" Of course, there is an argument to be made for this sort of thing, but at the same time if shortcomings are only apparent to you, then what does it matter? If your friend doesn't know you didn't brush your teeth, then how can you be positive that your interviewer noticed?
Insecurity is a tough monster to face. The hardest part about dealing with it is that its one of the few things that you actually do have to face alone. Depression you can remedy by finding the right people, but insecurity must be tackled by recognizing that there are two voices in your head: one that wants you to succeed, and one that tries to tear you down. If you can face it head on, you're one step closer to conquering it.
So, even if you don't believe me, let me just say it flat out. You did well on your interview. You look pretty dang good today, and one day, you will be successful. Don't let yourself say anything different, okay?