When was the last time you were faced with a real challenge? I'm not talking about a work problem that may have been an inconvenience that disrupted your day. I'm talking about true, life-altering challenges.

For the founder of Baby Einstein, Julie Clark, within a few years of selling her $23 million generating business to Disney for $25 million-- who turned it into a $300 million product line within two years-- she was diagnosed for a second time with cancer, though this time Stage 4. The mother of two shared on the Unmessable show that she was fighting for her life and in the process, made a conscious decision to spend all of her time and energy to heal her body, instead of feeding the disease.

She even authored a children's book to help parents communicate with their children about the illness and inspire them to participate in their recovery. Instead of surrendering her life to the diagnosis, she generated her own prognosis and won. Unquestionably, her journey proved to be the ultimate mental challenge.

How did Clark remain positive when it seemed like the world was caving in on her? What was her mindset that allowed her to turn her situation around in a miraculous way, while close friends, with similar diagnoses, passed? What are some things you can do to ensure a strong mindset as you embark on major mental challenges like building a business, a family or a legacy?

Clark says, the answer is simple in theory but difficult in practice and suggests these four exercises as a starting point.

Choose your reaction.

You can always choose, regardless of the situation, who you are going to be in the face of adversity. You cannot control the outcome, situation or other people, but you always have a choice to choose who you will be.

Instead of wasting your energy in modeling out all the million what if scenarios that might happen, and feeling bad for yourself--playing the victim-- use that energy for something that will actually make a difference. In Clark's case, she choose to fight her Stage 4 cancer with every ounce of energy she had and avoided letting her mind drift into a dark place that could drag her down. By obsessing over her recovery, her actions and intentions were channeled in that direction.

Define your goals and visualize the outcome.

It's not enough to have goals. You need to create a plan of action and stand in the visual of how it turned out. Clark would spend hours visualizing her daughter walking down the aisle. That was the image she held onto and was committed to realizing.

So start from where you want to end up and work your way to where you are today. Doing this exercise will make the action plan clear.

Make time for just being.

The world is a loud place. It's your responsibility to find the quiet. Clark credits meditation and being outdoors as her tool to being centered amid the chaos. This is an important part of developing a strong mindset.

Meditating can reduce stress, promote emotional health, enhance self-awareness, improve sleep, help to control pain and more. From morning meditation to nature walks or whatever works for you, segmenting just a few minutes to yourself will help you recharge, refocus, and recommit yourself to true intentions every day.

Set a powerful intention.

Setting an intention, as Gary Zukov mentions in his book, The Seat of The Soul, sets the stage energetically. Another way of looking at it is it by setting your intention, you set the context upon which you will operate, which is very powerful.

Clark's go-to intention: gratitude. It was particularly hard when she lost her hair and breasts, then friends to cancer, but today, gratitude is something she cannot live without.

Derive strength from your community.

A strong support system you can rely on will prove to be a powerful tool as you strive to lead with a strong mindset. From your spouse to your children, and maybe even your parents, the more people you can look to for comfort when times are hard, the better chances you have of navigating that period unscathed.

While facing a terrifying cancer battle, Clark was inspired to pen the novel, You Are The Best Medicine, a tribute to her children, who at a young age were able to help her maintain a strong mindset in the face of possible death.

Developing a strong mindset takes practice, but as most top performers will attest, it's worth the effort. Just as when you go to the gym, if you're committed to being fit, you will need to develop your strength and endurance over time. Strong leadership is about exercising your mental muscle to work for you.