An Egyptian librarian once heard that the sun could be seen shining at the bottom of a well in the town of Syene on the longest day of the year. He surmised that to make a reflection in a well, the sun had to be directly overhead on that day. And a sun directly overhead would cast no shadows from upright columns or posts. Yet on the longest day of the year in the city of Alexandria, where he lived, he observed that straight columns did cast shadows.

He decided to travel the 800 kilometers to Syene himself to verify that what he had heard was true. At midday on the longest day of the year, he looked into the well and saw the sun reflected. And sure enough, the posts in Syene cast no shadows. He reflected on that. After a while, he began to see a bigger picture of what these seemingly unconnected facts meant. Surprisingly, it went against what nearly everyone believed at the time. You see, the librarian’s name was Eratosthenes, and he lived more than 2,200 years ago.

As the director of the greatest library in the world (the library of Alexandria in Egypt was said to possess hundreds of thousands of scrolls), Eratosthenes was at the intellectual capital of the world for his time. In the third century B.C., nearly every scholar in Alexandria and around the world believed that the earth was flat. But Eratosthenes reasoned that if the sun’s light came down straight and the earth was flat, then there would be no shadows in both Alexandria and Syene. If there were shadows in one location but not the other, then there could be only one logical explanation. The surface of the earth must be curved. In other words, the world must be a sphere.

That’s a pretty impressive mental leap, although it seems perfectly logical to us today. After all, we’ve seen pictures of our planet from space. But Eratosthenes made that big-picture connection by using everyday facts and putting them together. What’s even more impressive is that he took it a step further. He actually calculated the size of the earth! Using basic trigonometry, he measured the angle of the shadows and calculated that it was approximately 7.12 degrees. That’s about 1/50th of a circle. And he reasoned that if the distance between Syene (modern-day Aswan) and Alexandria was 800 kilometers, then the earth must be around 40,000 kilometers in circumference (50 x 800 kilometers). He wasn’t far off; the actual circumference of the earth through the poles is 40,008 kilometers. Not bad for a guy who had nothing but his brain and a big-picture mindset to figure the whole thing out!

In the actions of Eratosthenes, you can see the truth of a statement made many centuries later by German statesman Konrad Adenauer: “We all live under the same sky, but we don’t all have the same horizon.” If you desire to seize new opportunities and open new horizons, then you need to add big-picture thinking to your abilities. People do not become successful without that ability. To become a good thinker better able to see the big picture, keep in mind the following:

1. Don’t Strive for Certainty

Big-picture thinkers are comfortable with ambiguity. They don’t try to force every observation or piece of data into pre-formulated mental cubbyholes. They think broadly and can juggle many seemingly contradictory thoughts in their minds. If you want to cultivate the ability to think big picture, then you must get used to embracing and dealing with complex and diverse ideas.

2. Learn from Every Experience

Big-picture thinkers broaden their outlook by striving to learn from every experience. They don’t rest on their successes, they learn from them. More importantly, they learn from their failures. They can do that because they remain teachable.

Varied experiences—both positive and negative—help you see the big picture. The greater the variety of experience and success, the more potential to learn you have. If you desire to be a big-picture thinker, then get out there and try a lot of things, take a lot of chances, and take time to learn after every victory or defeat.

3. Gain Insight from a Variety of People

Big-picture thinkers learn from their experiences. But they also learn from experiences they don’t have. That is, they learn by receiving insight from others—from customers, employees, colleagues, and leaders.

If you desire to broaden your thinking and see more of the big picture, then seek out mentors and counselors to help you. But be wise in whom you ask for advice. Gaining insight from a variety of people doesn’t mean stopping anyone and everyone in hallways and grocery store lines and asking what they think about a given subject. Be selective. Talk to people who know and care about you, who know their field, and who bring experience deeper and broader than your own.

4. Give Yourself Permission to Expand Your World

If you want to be a big-picture thinker, you will have to go against the flow of the world. Society wants to keep people in boxes. Most people are married mentally to the status quo. They want what was, not what can be. They seek safety and simple answers. To think big-picture, you need to give yourself permission to go a different way, to break new ground, to find new worlds to conquer. And when your world does get bigger, you need to celebrate. Never forget there is more out there in the world than what you’ve experienced.

From the How Successful People Think Workbook