After studying over 500 millionaires, including Andrew Carnegie, Henry Ford, and Charles M. Schwab, journalist and author Napoleon Hill found that they shared a single quality: decisiveness.

"Analysis of several hundred people who had accumulated fortunes well beyond the million dollar mark disclosed the fact that every one of them had the habit of reaching decisions promptly," Hill wrote in his 1937 classic, "Think and Grow Rich."

In addition to making decisions quickly and confidently, they also change decisions, if and when needed to, slowly, Hill noted. On the flip side, "People who fail to accumulate money, without exception, have the habit of reaching decisions, if at all, very slowly, and of changing these decisions quickly and often."

Decisiveness plays such an important role in accumulating wealth that mastery of procrastination — which Hill defined as the opposite of decisiveness — is the seventh of his 13 steps toward getting rich.

To become a better decision-maker, start by focusing on your listening skills, Hill explained:

Keep your eyes and ears wide open — and your mouth closed — if you wish to acquire the habit of prompt decisions. Those who talk too much do little else. If you talk more than you listen, you not only deprive yourself of many opportunities to accumulate useful knowledge, but you also disclose your plans and purposes to people who will take great delight in defeating you, because they envy you.

Your actions count more than your words. "Tell the world what you intend to do, but first show it," Hill wrote.

If you do master this quality, it can reap incredible rewards, Hill observed: "Those who reach decisions promptly and definitely know what they want, and generally get it ... The world has the habit of making room for the man whose words and actions show that he knows where he is going."

Since Hill's time, others have pinpointed qualities and habits shared among people who make millions, such as rising early, exercising regularly, making the time to read, and associating with others who are successful.

Read more: