Answer: Successful people have “formed the habit of doing things that failures don’t like to do,” according to Albert E.N. Gray.

Albert Gray wrote up his “discovery” in 1940 in this six-page essay The Common Denominator of Success.

Here is how Gray’s essay opens:

The Common Denominator of Success

by Albert E.N. Gray

Several years ago I was brought face to face with the very disturbing realization that I
was trying to supervise and direct the efforts of a large number of men who were trying
to achieve success, without knowing myself what the secret of success really was. And
that, naturally, brought me face to face with the further realization that regardless of what
other knowledge I might have brought to my job, I was definitely lacking in the most
important knowledge of all.

Of course, like most of us, I had been brought up on the popular belief that the secret of
success is hard work, but I had seen so many men work hard without succeeding and so
many men succeed without working hard that I had become convinced that hard work
was not the real secret even though in most cases it might be one of the requirements.

And so I set out on a voyage of discovery which carried me through biographies and
autobiographies and all sorts of dissertations on success and the lives of successful men
until I finally reached a point at which I realized that the secret I was trying to discover
lay not only in what men did, but also in what made them do it.

I realized further that the secret for which I was searching must not only apply to every
definition of success, but since it must apply to everyone to whom it was offered, it must
also apply to everyone who had ever been successful. In short, I was looking for the
common denominator of success.

And because that is exactly what I was looking for, that is exactly what I found.

But this common denominator of success is so big, so powerful, and so vitally important
to your future and mine that I’m not going to make a speech about it. I’m just going to
“lay it on the line” in words of one syllable, so simple that everyone can understand them.

The common denominator of success — the secret of success of every man who has ever
been successful — lies in the fact that he formed the habit of doing things that failures
don’t like to do.

It’s just as true as it sounds and it’s just as simple as it seems. You can hold it up to the
light, you can put it to the acid test, and you can kick it around until it’s worn out, but
when you are all through with it, it will still be the common denominator of success,
whether you like it or not.

It will still explain why men have come into this business of ours with every apparent
qualification for success and given us our most disappointing failures, while others have
come in and achieved outstanding success in spite of many obvious and discouraging
handicaps. And since it will also explain your future, it would seem to be a mighty good
idea for you to use it in determining just what sort of a future you are going to have. In
other words, let’s take this big, all-embracing secret and boil it down to fit the individual
you.

If the secret of success lies in forming the habit of doing things that failures don’t like to
do, let’s start the boiling-down process by determining what are the things that failures
don’t like to do. The things that failures don’t like to do are the very things that you and I
and other human beings, including successful men, naturally don’t like to do. In other
words, we’ve got to realize right from the start that success is something which is
achieved by the minority of men, and is therefore unnatural and not to be achieved by
following our natural likes and dislikes nor by being guided by our natural preferences
and prejudices.

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Of course, whether Gray’s answer is the definitive answer can’t be proven, but his idea sure gets a lot of support from other great thinkers:

Men’s natures are alike. It is their habits that carry them far apart. (Confucius)

Success is the sum of small habits, repeated day in and day out. (Robert Collier)

We are what we repeatedly do. Excellence, therefore, is not an act but a habit. (Aristotle)

Watch your thoughts; they become words. Watch your words; they become actions. Watch your actions; they become habits. Watch your habits; they become character. Watch your character; it becomes your destiny. (Lao-Tzu)