Exactly! You can't just pick a random quirk off the list and give it to your character. There should be a REASON they do that.

For example, I literally suck on my bottom lip (the way some people suck on thumbs). It's a habit I got into when I was a toddler and split open my lip to the point it needed stitches. That's when the habit began and I've always done it. It's not part of my character, but there is a valid reason for that particular habit of mine. It's not just something I picked up one day.

Of course, not every quirk has a definite reason. I twirl my hair and rub it against my cheek when I'm distracted (often at the same time I'm sucking on my lip). There's no real reason for this except I've almost always had long hair and my hair is pretty soft (gotten lots of comments on it). I also will rub soft/silky materials against my cheek for the same reason, often without thinking. My girls have satin trim on their lovey blankets and I've caught myself rubbing the satin between my fingers and I have run it along my cheek more often than I care to admit. Something about that texture draws me in.