Chastity
Luna Lovegood was lucky. She didn't have the same kind of urges to get in bed with a boy that some of her fellow students had. Luna could never understand how, or why, many of the other girls were so eager to "land a husband," with Romilda Vane, Lavender Brown, and Luna's fellow Ravenclaw, Cho Chang, being some of the most desperate to fall in love. They would even go so far as to try a love potion to get what they wanted!
Couldn't they all see that listening to your hormones instead of your head leads to all kinds of stress, family problems, unwanted pregnancies, and sometimes, STDs? And Headmaster Dumbledore had always warned that to coerce love with a potion made babies who grew up to be people who lived without love, like You-Know-Who.
First of all, Luna was a Ravenclaw. Ravenclaws think before they act, or at least they should. And she had though about what she wanted to do with the people in her life who appreciated her, and how to react to those who didn't. She was content just to have some friends, knowing that marriage was something sacred, something special to be treasured, and she was not the right age for marriage yet. Besides, it's been proven numerous times that love potions don't create true love, only infatuations and obsessions, so who in their right mind would use a love potion to get their lover?
And as for the people who scorned her, she had learned long ago to just ignore those folks and be herself, because, as one of the most original Ravenclaws of her time, she was the most honest with other people.
"I heard about how Romilda Vane tried to slip you a love potion, Harry," she said to one of her best friends.
"Yeah," said Harry Potter, "That witch just won't give up."
"Don't worry, Harry," Luna reassured him, "You're just as sane as I am to know that love potions are not good. And you have the brain to figure out what a premature love relationship can lead to, also. Besides the usual things that Muggles also worry about, those naughty Nargles like to poison such relationships by manipulating the crotches and spiking the semen during sex."
Harry looked at her, wide-eyed at her seeming sense of humor, but he could tell she was quite serious, and quite honest. "I have no doubt we'll both find the right partner someday, Luna," he said.
And years later, when Luna married Rolf Scamander, and Harry married Ginny Weasley, while Romilda Vane and some other girls had messed up with some of their romantic partners, Luna knew one thing. True love comes through chastity, not lust.