There's a pervasive belief that mental illness stems from weakness. But that's not true.

Unfortunately, however, the belief is so widely held that some people don't recognize that they're attaching a stigma to mental illness.

When I wrote my book about mental strength, I received comments from people accusing me of stigmatizing mental illness by talking about mentally strong people. They assumed mentally strong people couldn't have a mental illness.

But the truth is, many individuals who have a mental illness are mentally strong. In fact, some of the strongest people I've ever met were those who entered my therapy office seeking help for illnesses, like PTSD or depression.

Those who assume otherwise don't understand mental strength. And they certainly don't understand mental illness.

Mental Illness Isn't Treated the Same as Physical Illness

When someone develops a physical illness, like cancer, no one ever says, "He wasn't physically strong was he?" Instead, we look to things like genetics, the environment, and the person's immune system.

While it's clear that a nutritious diet, plenty of sleep, and regular exercise can prevent some health issues, some physical illnesses aren't 100 percent preventable. From the common cold to Alzheimer's, science hasn't given us a full-proof plan to prevent all illness.

Fitness guru Bob Harper is a perfect example of this. As a personal trainer best known for his role as a coach on the Biggest Loser, Harper appears in a variety of workout videos and he's authored many books about diet and fitness.

A few weeks ago, Harper experienced a heart attack. Yet, no one questioned his commitment to good health. Instead, people used his story as a reminder that you can't control your genes.

Wouldn't it be nice if we did the same for people with mental illness? Instead of gossiping about someone who is hospitalized for anxiety or blaming someone with depression for being lazy, what if we applauded them for staying strong?

A healthy lifestyle can go a long way to preventing mental illness. But, just like you can't prevent all physical illness, you can't prevent all mental illness.

And people who have a mental illness can be just as strong--even stronger--than someone who doesn't. Just like someone who has diabetes can still be physically strong, a person with depression could be very mentally strong. After all, someone with a mental illness has several complicating factors that make it even more difficult to develop mental muscle.

We Need to Talk More About Mental Strength

Talking about mental strength isn't about shaming people with a mental illness. Instead, it's about encouraging a healthy lifestyle that could prevent some mental health problems.

Holding more conversations about the habits that develop mental muscle can reduce the stigma associated with mental illness. It can also encourage people to seek help if they experience symptoms or warning signs.

And it's important to note that mental strength isn't the same as acting tough--it's not about seeing how much suffering you can endure. Instead, it's about taking the steps to reach your greatest potential, which often involves asking for help when you need it.