When Amy Morin was 23, she lost her mother suddenly to a brain aneurysm. Three years later, the night before the anniversary of her mother’s death, her 26-year-old husband died of a heart attack.

In the wake of such loss, Morin, a social worker and psychotherapist, worked hard to deal with her grief and move on: She moved to a new home, started a new job as a counselor in a medical practice, and eventually re-married. And then, just as everything seemed to be going so well, her beloved father-in-law was diagnosed with cancer. The prognosis wasn’t good.

RELATED: 12 Worst Habits For Your Mental Health

In an effort to steel herself against yet another staggering loss, Morin sat down at her table and wrote a sort of letter to herself—a list of the habits that she knew would weigh her down if she let them. The list included everything from fearing change to agonizing over circumstances beyond her control. She turned the list into a blog post, which went viral; then expanded it into a book, out now, called 13 Things Mentally Strong People Don’t Do ($27, amazon.com).

I asked Morin, based on her personal and professional experience, which of her 13 habits are the most common traits people struggle with and what to do about them. Here, she identifies three challenging but crucial habits that can help you build resilience, so you can better weather what life throws at you.

They don’t feel sorry for themselves

Self-pity is one of the most natural responses when bad things happen, which is why so many people struggle with this one, Morin says. But mentally strong people know that wallowing for too long is self-destructive and a waste of time. “Focusing on an injustice provides an excuse to dwell on a problem,” she explains. “Instead, we need to find a way to move forward even when we don’t feel like it.” If pity starts to creep into your thoughts, try to do something active that is the exact opposite of how you feel, she advises in the book. It doesn’t need to be big—go for a run or do an active favor for your elderly neighbor, like offering to mow her lawn. Either one of these can help you switch gears because they'll boost your mood. This interruption is what you need to start proactively seeking a solution to your problem, she says.

RELATED: 12 Ways We Sabotage Our Mental Health

They don’t expect immediate results

Our fast-paced culture sets us up for impatience. “When we don’t see results fast enough, it’s easy to conclude we’re not making progress,” says Morin. Not wanting to wait may lead you to take shortcuts or give up on a goal altogether. “But long-lasting change is a marathon—not a sprint,” she says. In her book, she suggests several ways to help you stay on track (whether you’re trying to lose weight or build a business). One simple strategy involves marking milestones along the way to your finish line: Create smaller objectives and celebrate as you reach them to remind yourself of the progress that you are making. If you’re able to commit for the long haul, you’ll be more likely to eventually succeed.

RELATED: How to Plan for Weight Loss Success

They don’t resent other people’s success

People struggle with this one because it often masks another, underlying issue: We tend to feel jealous of what other people have when we aren’t sure about what we want for ourselves, Morin says. You might covet a friend’s cool job or jetsetter lifestyle, for example, without considering if that’s what would truly make you happy. “We need to stay focused on our own definition of success,” says Morin. To gain a better understanding of your hopes and dreams, she recommends asking yourself what would make you the most proud and bring you the most peace when you look back at the end of your life. Write it down. The next time you start to feel envious of someone, remember that she is working toward her personal goals, and that you have different ones. “Try to keep in mind that everyone’s journey is unique.”

RELATED: 9 Ways to Silence Your Inner Critic