As the author of 13 Things Mentally Strong People Don't Do, I usually spend my time talking about the bad habits that can rob you of mental strength. After all, it only takes one bad habit to hold you back from reaching your greatest potential.

In addition to giving up those bad habits, however, it's also important to perform exercises that build your mental muscle. With hard work and dedication, you can train your brain to perform at your peak.

Here are 18 things mentally strong people do.

1. They practice gratitude.

Counting their blessings, rather than their burdens, helps mentally strong people keep life in proper perspective. Their choice to be grateful shines through in their mood and behavior.

2. They retain their personal power.

Mentally strong people don't give negative people power over them. They refuse to blame anyone for holding them back or dragging them down.

3. They accept challenges.

Mentally strong people view adversity as an opportunity to grow stronger. With each obstacle they overcome, they gain confidence in their ability to become better.

4. They focus on the things they can control.

Mentally strong people stay productive and effective by focusing on the things they have control over. Rather than waste energy worrying about whether the storm will come, they invest their efforts into preparing for it the best they can.

5. They set healthy boundaries.

Creating healthy emotional and physical boundaries gives mentally strong people the room they need to grow. Even when they may disappoint others, they're willing to say no.

6. They take calculated risks.

Mentally strong people balance their emotions with logic so they can calculate each risk they face. They're willing to step outside their comfort zone and seek opportunities that will help them reach their goals.

7. They make peace with the past.

Mentally strong people reflect on the past so they can learn from it, but they don't dwell on it. They refuse to live a life of regret and they let go of grudges.

8. They learn from their mistakes.

Rather than beat themselves up for their mistakes, mentally strong people focus on learning from them. They accept full responsibility for their behavior and choose to move forward in a productive manner.

9. They create their own definition of success.

Rather than resent other's good fortune, mentally strong people feel free to share in their joy. They recognize that other people's achievements don't diminish their own.

10. They view failure as an opportunity for growth.

Failure is often part of any long journey toward success. Mentally strong people accept that and they choose to use each failure as an opportunity to grow wiser.

11. They set aside time to be alone.

Mentally strong people take time to be alone with their thoughts. Whether they write in a journal, practice meditation, or sit silently and reflect, they know a little solitude is essential to their well-being.

12. They accept full responsibility for their lives.

Mentally strong people create opportunities for themselves. They don't waste time waiting for the world to give them what they think they're owed.

13. They practice perseverance.

Mentally strong people know that the best things in life are worth waiting for. They exercise patience and persistence as they strive for their goals.

14. They modify their unhealthy beliefs.

Mentally strong people refuse to allow self-limiting beliefs to restrict their potential. They understand their minds can be their best asset or their worst enemy.

15. They expend their mental energy wisely.

Instead of complaining about things they can't change or rehashing something that happened yesterday, mentally strong people devote their energy to productive tasks. They don't waste limited resources, like time and energy, on things that aren't helpful.

16. They practice realistic optimism.

Mentally strong people talk to themselves like a trusted coach. They refuse to believe pessimistic predictions but they also don't allow themselves to become overconfident.

17. They tolerate discomfort.

Mentally strong people aren't afraid to endure a little pain. Whether they keep running when their legs are tired or they resist instant gratification, they practice self-discipline even when it's uncomfortable.

18. They stay true to their values.