This is a story about some of the most successful people in the world -- from the famous to the unknown -- and the one single thing they almost all do.

Bottom line: They pick something they care about, and they do small pieces of it over and over and over before anyone else pays even the slightest bit of attention.

Then, with luck, they ultimately build it into a success.

I thought of all this recently after reading one of the more unusual profiles I've seen in the New York Times, about an Australian writer named Matt Zurbo who decided to honor his baby daughter by writing 365 children's books in a single year.

He writes mostly at night, after he's put in a full day doing hard physical work farming oysters (which is how he pays the bills).

None of the stories has been published (yet, anyway), but they're quite good -- good enough to convince a Times reporter to travel to Tasmania and follow him around for four days to learn how he works.

That prompted me to realize I'm about to hit a small milestone of my own for 2019: By this weekend, I will have written 250 articles for since January 1.

Between all those articles -- along with book projects and work for other publications -- I've been able to interview, study, and write about thousands of very successful people from all walks of life.

And I keep coming up with that one realization.

It's a truism that everything seems inevitable in retrospect -- even things that were really hard and unlikely at the time.

But, it wasn't really all that likely that say, Jeff Bezos would build Amazon out of nothing.

Or that Sara Blakely would go from unhappy fax machine salesperson to the billionaire founder of Spanx, or that Jerry Seinfeld would become one of the best-known comics of all time.

Or that Ed Sheeran would wind up the most successful touring musician in history, or that Tom Brady would go from also-ran, sixth-round draft pick to the greatest player in NFL history.

Or that the parents of a six-year-old would build the most financially successful Youtube channel of all time, or Bill Gates would build Microsoft, or frankly that the Founding Fathers would have succeeded in establishing the United States of America.

But they all succeeded, in part because during the early days, when nobody was paying them any attention, they just started doing the work. One day became two, which became 10, then 50, and 500.

Then they seemed like overnight successes.

I don't mean to suggest that this "just do it" mentality was the only ingredient. Obviously not.

But it was a necessary one. And it's also the one that so many less successful people just don't understand -- or that they think is simply unrealistic. 

It's hard to imagine what the future will really look like, and what success will actually be, when you're slogging through yet another day of doing things you feel strongly about -- when nobody else even notices yet. 

But it's also one of the keys to success: day after day after day.