Cicero referred to curiosity as a “passion for learning.” Writing about the outstanding brilliance and peculiarity of his subject, historian extraordinaire Walter Isaacson discusses curiosity in his biography of Leonardo da Vinci,

In addition to his instinct for discerning patterns across disciplines, Leonardo honed two other traits that aided his scientific pursuits: an omnivorous curiosity, which bordered on the fanatical, and an acute power of observation, which was eerily intense. Like much with Leonardo, these were interconnected. Any person who puts “Describe the tongue of the woodpecker” on his to-do list is overendowed with the combination of curiosity and acuity.

His curiosity, like that of Einstein, often was about phenomena that most people over the age of ten no longer puzzle about: Why is the sky blue? How are clouds formed? Why can our eyes see only in a straight line? What is yawning? Einstein said he marveled about questions others found mundane because he was slow in learning to talk as a child. For Leonardo, this talent may have been connected to growing up with a love of nature while not being overly schooled in received wisdom.

…His curiosity was aided by the sharpness of his eye, which focused on things that the rest of us glance over…. The acuteness of his observational skill was not some superpower he possessed. Instead, it was a product of his own effort. That’s important, because it means that we can, if we wish, not just marvel at him but try to learn from him by pushing ourselves to look at things more curiously and intensely.

In his notebook, he described his method—almost like a trick—for closely observing a scene or object: look carefully and separately at each detail. He compared it to looking at the page of a book, which is meaningless when taken in as a whole and instead needs to be looked at word by word. Deep observation must be done in steps: “If you wish to have a sound knowledge of the forms of objects, begin with the details of them, and do not go on to the second step until you have the first well fixed in memory.

Isaacson’s previous biographical subjects include Albert Einstein, Benjamin Franklin, Ada Lovelace, and Steve Jobs—all blue-sky thinkers, with insatiable, lifelong appetite for knowledge and the ability “to make connections across the disciplines” and “to marry observation and imagination.”