We tend to think of people who have true grit and exceptional perseverance as hard -- they have a thick enough skin and strong enough emotional defenses that whatever life throws at them, it simply bounces off.

If you view mental toughness through this prism, it's easy enough to extrapolate how to develop more of it -- challenge yourself, take more knocks, and you'll learn to persevere even when it hurts. But according to a couple of thought-provoking recent articles, this is the pretty much the exact opposite of the truth about real resilience.

The heart of exceptional mental toughness, these writers argue, isn't the ability to shut the world out, but a desire to engage it. True grit comes from passion -- from love -- not from emotional hardness.

Passion is the root of exceptional perseverance.

In the New York Times recently, columnist David Brooks makes this case in relation to today's "coddled" college students. Many argue that what emotionally fragile undergrads need to develop some grit, Brooks writes, is to take a few more lumps early in life, rather than being constantly protected by helicopter parents.

But while there may be grounds to criticize this popular parenting style, Brooks insists that what really afflicts fragile young people isn't a lack of experience of hardship, but a lack of purpose. What drives people to do truly tough things is a truly great cause.

"The people we admire for being resilient are not hard; they are ardent. They have a fervent commitment to some cause, some ideal or some relationship. That higher yearning enables them to withstand setbacks, pain and betrayal," he writes. Civil rights leader John R. Lewis, for example, may not have been born with inherent grit, but he was driven to exceptional mental toughness by his passion for justice.

We need to put aside the world-weary cynicism and detachment popular with young people, pleads Brooks: "If you really want people to be tough, make them idealistic for some cause, make them tender for some other person, make them committed to some worldview that puts today's temporary pain in the context of a larger hope."

Don't confuse grit and fear of failure.

Writing for the Greater Good Science Center, positive psychology expert and author Christine Carter makes much the same point, though she uses more practical and less philosophical language to do it.

"We admire or foster a character trait we call 'grit' but that is really relentless, persistent perfectionism, absent the intrinsic motivation," she cautions those concerned with fostering mental toughness. What we should be encouraging is the passion that drives us to persevere through even the toughest difficulties, not an abstract commitment to never giving up and always being perfect.

"If you are a parent or teacher looking to foster grit in kids, the first step is to let go of what you want for them, and watch for what they are passionate about. Then, simply support their passions," she advises.

In other words, if your aim is to increase your grit (or help others increase theirs), the first step is finding your passion, your true belief, your love.

Do you agree with this analysis of what's at the heart of true grit?