Did you ever have one of those days when you just feel discouraged, unambitious, and just tired? Occasionally, it may turn out to be a day you just want to pull the blankets back up over your head.

It's nothing to be ashamed of. It happens to the best of us--whether you're a pro athlete or a successful entrepreneur. After all, motivation waxes and wanes.

Developing mental strength can help keep us motivated so that we can move forward towards accomplishing our goals. But how can you build mental strength in order to stay motivated? Start with these five tactics that I use in my life to stay mentally strong while remaining motivated at work.

1. Spend at least 15 minutes a day in quiet reflection.

"A few minutes of quiet time gives you an opportunity to reflect on your progress and think about what you want to do better," writes Amy Morin, the author of 13 Things Mentally Strong People Don't Do.

She continues: "Schedule a few minutes every day to recharge your batteries with a little bit of solitude. It will help you gain clarity and renew your motivation to reach your goals."

I do this every morning by waking up before everyone else in my home. It gives me alone time to reflect on my progress, exercise, read, write in my gratitude journal, and plan my day. I personally like to do this at 5:15 a.m.

2. Say "No" without batting an eyelash.

"Friends, family, and business associates pull us in a million directions. It's easy to succumb to their will and work to make them happy," says Daniel Ndukwu, founder of The Experiment.

He goes on to say: "It's much harder to tell them 'no' because we don't want to hurt their feelings or be seen as someone that's not a 'team player.' With mental strength comes the ability to make decisions that are best for you.

"Saying 'no' is liberating."

There is another rough side of life if you don't learn to say "no." What if you believe that you can't say "no" because you believe it will hurt business? This happens quite often if you're a freelancer.

Choncé Maddox suggests on Due that you can in fact say "no" by referring the client to another freelancer in your niche. You can also be straightforward by saying that you currently have a full plate and aren't accepting new clients. If the client is flexible, you can offer to work with them when you have the availability.

3. Help and inspire others.

"Maybe you wonder how this can benefit you. Remember that helping people will bring you satisfaction," writes Silvia Turonova on Motivation Grind.

"Part of becoming stronger and sure about yourself is feeling good. If you inspire people, you will be inspired as well. You will grow personally. You will see the best of you become even better and you will become motivated."

Silvia adds, "If you are excited and happy, you automatically feel more courageous to take a challenge. Being undefeatable is the state of mind, and feelings are an important part of it."

Personally, I've been working with the Open to Hope Foundation for the last several years. Open to Hope has a clear focus on helping those who have lost a loved one.

More than that, this foundation has helped many thousands find hope following a tragedy by being the rock that people can lean and rely on.

You can help inspire others in your own circles. When you work on learning how to defeat your own fears, you begin to become a little more invincible to lessor stressors. In this sense, you gain some self-power to deal with life.

4. Focus only on what you can control.

"Yes, we play to win, that's why we keep score. But spending time thinking about the potential outcome just diverts your focus and fills your head with unimportant, distracting thoughts," writes Joel Brown, the founder of Addicted2Success.

"The remedy is to be present in the moment and let nature take its course. Focus only on the things you actually control: your approach and your attitude. What happens after the next point or after the match doesn't matter."

Joel says that "this approach helps me relax, focus, and play my best at the key moments."

5. Eliminate fear and self-doubt.

Although she was specifically discussing training, this advice from hypnotherapist and counselor Emily Hughes also applies to anyone wanting to remain mentally strong and motivated:

"Fear and self-doubt are your mental strength's biggest enemies. To combat this and protect your mental strength, these two enemies need to eliminated.

"Firstly, you need to identify what your self-doubts, fears, and concerns are. Then you can begin to start letting them go, and a simple visualization is the perfect tool for this. As you release those doubts and fears from your mind, it allows your motivation and mental strength to remain solid and strong.

"To further strengthen yourself, you can visualize your end goal just the way you want it be. Allow this concept to be your point of focus, rather than any self-doubt and fear."