If you have been in business any length of time, chances are you've “bonked.” This refers to a phenomenon that happens to marathoners around mile 20 that's otherwise known as “hitting the wall.”

Succeeding in business is much like a marathon: The start is exciting, with the thrill of anticipation swelling as you toe the starting line. You know where you want to go, and you're committed to getting there. The end is equally exciting. Actually seeing the finishing line in the distance brings on a surge of adrenalin; it's easier to finish the race with the end in sight. Between the excitement of the start and the rush of the finish comes the toughest part of all: the middle miles.

These requisite, unavoidable middle miles can be a desolate wasteland or they can be the most productive miles of the race—it's how you deal with them that determines if and when you cross the finish line, and in what kind of shape…winning in business is no different. It's no wonder that during a business middle mile there's a huge temptation to quit.

This is the often precarious, volatile and risk-intensive stretch of one's company or career that lies between the excitement of starting a new journey and reaching the end game objective, whether that be selling a business, taking a company public, becoming an executive or entrepreneur, securing a new position, pursuing a new career path, or retiring wealthy.

So how can you increase your professional endurance? Here, I've compiled five tips to help you persevere through that middle mile:

1. Keep Your Eyes on the Prize. The middle mile is the stuff in between, and where the real work gets done. It's the time in your business or career journey where you burn the most energy, deal with fatigue and hopelessness, work through budgetary and employee concerns, embrace setbacks and do your best to overcome burn-out. It's in this period when there's a huge temptation to quit. Lack of discipline, poor implementation, and failure to simplify are the three primary reasons, but beneath those symptoms is the underlying failure: Losing sight of the finish line. Keep your eye on where you ultimately want to go.

Remember that you didn't get to the middle mile without effort. You've put in some hard work, but suddenly you are not advancing nearly as fast as you would like. This critical time is when the best “athletes” trudge forward with new training methods, better work ethic, and by stretching imagination and willpower. Committed professionals neither quit during the middle miles nor do they settle for “good enough.”

The formula is pretty simple. Have a no-nonsense attitude; work hard; and improve every day. Arrive early and stay late if that's what it takes. Many professionals get stuck in the middle for the simple reason they don't work hard enough to get out of it. No one needs to convince a distance runner wake up early, lace up those running shoes, and go. To be successful, you must have the discipline to do what others don't want to do. Have a plan and work it every day.