Richard Branson, founder of Virgin Group, has said in interviews, "My biggest motivation? Just to keep challenging myself."

Long after the thrill of starting a business is gone and you are immersed in the daily challenges of being an entrepreneur, it is easy to lose the motivation to keep going. Being a business owner has its indisputable benefits, but it is a grind and you constantly need to remind yourself why you decided to become an entrepreneur.

A successful entrepreneur's number-one asset is perseverance. When I asked around to learn about what keeps entrepreneurs motivated, ambition and perseverance are two words that kept coming up. The need to achieve and succeed prevented them from giving up after every failure and fueled their drive more than any other factor.

If you find it challenging to maintain your morale in the long run, look around you and identify the people who make up your success team. Whether it's an older mentor who keeps you in line with your goals, or a younger entrepreneur who inspires you and fuels your energy, surrounding yourself with business cheerleaders helps turn every setback into a lesson, not a disappointment.

If you are running a startup and your goal is to make a million dollars this year, then you might be setting yourself up for disappointment. Instead, set several smaller, measurable milestones so that you can track your progress.

Yes, having your own business means you're invested 24/7, but invested and overworked are two different things. There is nothing more daunting than spending your day alone in your home office. Make time to take care of yourself.

Business owner Sharon Middendorf says what keeps her motivated is "ambition, exercise and meditation. This inspires and guides me through the days."

Set regular times during the week to unplug, hang out with family and friends, sign up for a gym, take walks, read or watch TV. If possible, take a vacation! This gives your brain time to rest, recalibrate and be ready to run a successful business.