Character quirks: A literary tool or a reflection of real life?

Hello all!

I've said it before and I'll say it again, one of the best things that ever happened to me in my writing life was hearing J.A. Konrath speak at a conference and the sitting next to him at a book signing.  He changed my outlook on publishing and writing, and he kept me in the writing life.  I was definitely on my way out, ready to give up, before I met him.

One of the things he talked about in his seminar was character quirks.  In his fantastic alcohol series, his main character Jacqueline "Jack" Daniels has a myriad of personality quirks.  When writing a series, he told us, it's important to have your character have or do something that readers recognize as a character trait, something that winds up being part of the story one way or another.

I took that to heart.  If you read my books, and true, my "Rock Harbor Chronicles" books aren't so much a series as books with similar locales and characters, you'll find people who are all riddled with character traits and quirks.  And my most recent work, the start of my Nora Hill series, I find that my main character, Nora Hill, is a ball of walking, talking quirks.
The other night I was getting ready for bed and I put on a tank top, some call it a wife beater, under my t-shirt. I've been wearing this tank top for a while.  It's a nice extra layer for those nights when I need to slather an extra amount of baby oil or lotion for my skin.  Wearing two shirts instead of one

cuts down on the amount of seepage onto the sheets.  Yeah, that tank top is pretty ratty.  

Not that it ever fit me.  I didn't buy it. It sort of wound up in my laundry one day. I gave it to my daughter...not hears.  I thought it might belong to one of my son's friends, nope.  So now it's mine.

Except I'm pretty sure I know where it came from. 

A couple years ago my children befriended a girl who needed friends.  Her parents, divorced, had all but kicked her out of the house.  She worked where my daughter worked and she and her younger brother befriended my two children.  She spent many nights at my house, almost became one of the family.

Almost.  

Then one day she told my son she wanted to date him.  My son said he liked her, but they were friends and that was all they would ever be.  And that's when it all went wrong.  I can't prove any of it, but one day she showed up to work with fresh bruises on her arm, and told my daughter that my son had hit her.

My daughter believed her.  After all, who would lie about that?

Except for one thing:  Anyone who knows my son knows that the one thing he is passionate about is hating those who are violent to women and girls. When he was very young the father of a classmate of his threw a bowl of soup at his wife and hit my son's classmate.  The girl came to school, because it was the safest place for her to be.  My son never, ever forgave the man.  Violence against women and girls is the one thing he hates more than anything else.

After a short period of time, my daughter realized this.  She spoke out against her friend.  And her friend, a girl I'd fed and housed countless times, turned on my daughter and began bullying her mentally and physically at work.  My daughter had to quit her job because it was no longer safe for her to go to work.

That girl has since faded from our lives.  I don't know where she is and frankly I don't care.  So why do I keep the ratty tank top?  Why do I keep it close to me at night?

She was my worst nightmare, that girl. The power she had over my daughter for a time nearly tore the family apart and what she could have done to my family scares me to my core.  I keep the shirt to remind myself that life and peace is fragile and that even the tightest family bonds can be tested by a whispered word.  I hold on to that shirt to remind myself that not everyone who comes through my door is as kind hearted as we've raised our children to be.  Most of all, I keep the shirt to remind myself that knowing my children is the best thing I can do to defend them.

So is that a personality quirk?  If I were a character in a novel...and why wouldn't you want to write about me...this would be something that would come up, this ratty tank top.

Look around.  Everyone has something, be it a diagnosis or just something they do, that defines them, helps the world recognize them.  When we read books that involve characters like this, is it a good literary tool, something just for the purpose of making the character a well defined picture for us or is it a reflection of our own lives?