There are a lot of books that explore the essential traits and skills of highly successful salespeople. You can probably quickly call out a list of the qualities that they endorse--a strong focus on the customer, acute listening skills, the ability to manage the sales process, the credibility of a trusted adviser, accountability for delivering value, resourcefulness, and the list goes on.

But is there one sales trait that rules them all? Or, to put it another way, is there a trait without which you absolutely cannot succeed at sales? Anthony Iannarino, founder of The Sales Blog and author of the forthcoming book, The Lost Art of Closing (Portfolio, August 2017), says there is. The trait is self-discipline.

"Self-discipline is the difference between success and failure," wrote Iannarino in his previous book, The Only Sales Guide You'll Ever Need (Portfolio, 2016). "Yes, there are a lot of other components of the salesperson's mind-set, skill set, and tool kit, but without strong self-discipline, those don't matter one whit."

The Only Sales Guide You'll Ever Need​ offers up a "periodic table of sales." It describes 17 elements--nine behaviors and eight skills--that salespeople need to adopt and master to excel at their craft. Of course, the first element in the book is "me management"--the cornerstone of sales success.

"In sales, self-discipline is what separates the great from the mediocre," says Iannarino. Want to be a great salesperson? Here are five techniques that Iannarino says will help you develop the willpower, fortitude, and accountability required by self-discipline:

1. Create a discipline list

A discipline list breaks your sales goals down into actionable steps--what you actually need to do to hit your targets. Once you have a list of actionable steps, schedule them on a daily, weekly, and monthly basis, as needed. "Your discipline list might include spending the first hour of each day making calls to the hottest leads on your list, the best prospects in your territory, and the referrals you've picked up from existing clients," says Iannarino, who offers a free discipline worksheet on his website.

2. Schedule the worst things first

Self-discipline isn't a lot of fun for most of us, but it will seem a lot easier if you do the tough things first. "Instead of delaying your most difficult tasks, attend to them first thing in the morning, while you are still fresh and before the world starts distracting you with its demands," says Iannarino. "Finishing a difficult task gives you a burst of energy and makes it easier to tackle the next task. This is also a surefire way to build success momentum."

3. Write down your commitments

"Writing out your disciplines moves them from the ephemeral to the concrete," says Iannarino. Moreover, you can make that practice even more powerful by thinking about the positive outcomes you'll achieve if you meet your commitments, and the negative ones that will occur if you don't.

4. Make your commitments public

Nobody likes being thought of as unreliable and untrustworthy, so adding this risk can motivate you to stick to your discipline plan. "If you plan to prospect daily, which I highly recommend, publish your prospecting calendar as a way to gain support from your peers. Post the calendar on your door," suggests Iannarino. "It takes courage to make public commitments, but if you do, you'll reap even greater rewards by earning the confidence and trust of others when you keep these promises."

5. Eliminate distractions and stop multitasking

Distractions, including multitasking, are the archenemy of self-discipline--and we live in a world full of them. "As you work through your discipline list, eliminate all distractions and concentrate on one task at a time. Turn off your cell phone, close the Web browser, hang a Do Not Disturb sign on your doorknob, and devote all your attention and brainpower to achieving your goals," concludes Iannarino.