There's a movie out there called You Can Count on Me, which is about an adult brother and sister who have a troubled relationship. I didn't think it was a great film, but it does a really good job of capturing a certain sibling dynamic in which one kid (the sister, in this case) is The Good Kid, and the other kid (the brother) is The Bad Kid. Of course, The Bad Kid is only marginally more screwed-up than The Good Kid, but she's got it together enough to do things like hold down a job and stay out of jail that the brother can't seem to manage.

The whole Bad Kid/Good Kid pigeonholing is, naturally enough, very corrosive to their relationship as adults. That's captured in the first interaction you see between the two of them. They haven't seen each other in a while, and it should be noted that at this point, the audience knows that the sister (who has a son) is really struggling because she's a single mother who works, and she just got a new boss who's being a real dick and messing up her child-care arrangements for no good reason.

The conversation goes like this:

Terry [the brother/Bad Kid]: So how are ya?

Sammy [the sister/Good Kid]: I'm fine, Terry

Terry: So um... um, how's Rudy [her son]?

Sammy: We're fine, Terry. 

[beat] 

Sammy: How are you? 

Terry: Uhhh, yeaahhh... 

It's hard to capture the delivery, but when the sister says "I'm fine" or "We're fine" she's saying it very quickly, because what she's really saying to him is "We are not going to talk about that--we're going to talk about you, because you are the mess here."

The sister doesn't consciously mean to do this, but with her insistence that everything is fine, she's shutting her brother out of her life. She's not allowing him to sympathize with her or even to learn anything about her life--"I'm fine" presents him with a blank wall of superiority that has no handholds and no way in.

Think about that before you start creating characters who are all fine--confident and capable and unflappable and content and marvelous. With perfect teeth. And there's no self-delusion or naivete there--they honestly are totally fine and perfect!

For one thing, hello fantasy figure! I've known a lot of people whose lives look very good from the outside, but trust me, they have problems both big and small--think of Helen Harris III in Bridesmaids, Gaston in Beauty and the Beast, or more ominously, Vic Mackey in The Shield. Just because someone looks perfect, or worse yet, actually thinks they are perfect, doesn't mean they are perfect--in fact, it usually means quite the opposite.

For another thing, if your protagonist is Mr. Perfect Super Guy, why should I worry? I mean, he's clearly going to fix everything handily without ever breaking a sweat. He's never going to be wrong, or make a mistake, or worry that he might be wrong or might make a mistake. Everything's going to end happily for him--the bad guys will be defeated, and he will get laid lots and lots of times by hordes of fantastically beautiful women. Since I know all this without actually reading the book, why should I bother? You've built an impenetrable wall, and there's no way in.