The Royal Library of Alexandria, Egypt, was one of the largest and most significant libraries of the ancient world. It flourished under the patronage of the Ptolemaic dynasty and functioned as a major center of scholarship. The library was part of a larger research institution called the Museum of Alexandria, where many of the most famous thinkers of the ancient world studied.
The library was existent during the time when people considered the earth to be flat. Modern day ideologies were yet to be developed. In that era there was a scholar named Eratosthenes. He was the chief librarian of the great library of Alexandria. During his time at the library, he stumbled upon a scroll which mentioned that there was a well in Syene which was only lit at the longest hour of the longest day and all the objects had no shadow on that hour. But far away in Alexandria, he knew that there was no such phenomenon.
A trivial information which anyone would have ignored. But Eratosthenes thought if the earth was flat how that could be possible. There could be only two cases if the earth was flat. one that the there should be equal shadows in Syene and Alexandria or there should be no shadow in both the places. But how could there be different shadows at the same time in two different cities?
This perplexed him and he was not ready to accept that such phenomenon existed. But he said why someone would lie about such a trivial issue. After giving it a thought he concluded that the earth had to be round if the facts were correct. He didn’t stop there, though. He sent a man to pace out the distance between Syene and Alexandria. With the distance between the two places and difference in shadow length, he was able to calculate the circumference of the earth.
See the video by Carl Sagan to understand better.
Try putting yourself in his shoes would you have done the same. Do you dig your data deep? Do you consider small hints important? Have you come across instances where ignoring simple facts has caused disasters or hindered you from catching the next best thing?