It is said that Abraham Lincoln had a high-pitched voice with a shrill quality to it. When he began his speeches, the audience at first wondered if this tall man was indeed the great orator of whom they had heard.

But as Lincoln’s words washed over them and Lincoln fell into a rhythm, the audience was soon mesmerized — both by the words they heard and how they were delivered.

When Harvard Business School Professor Clayton Christensen began a speech, it was similar. Instead of thunder and lightning, his speech was slow and methodical, soft and unassuming. But as Christensen — a tall man himself at 6′ 8″ — dove into his stories and began teaching how the world worked, he gained steam and cast a spell over a mesmerized audience.

When I shared this observation with Christensen — or Clay, as I called my mentor, friend, coauthor, and cofounder — he discounted it, with his characteristic humility. But that isn’t to say it wasn’t true.

In the hundreds of instances I saw Clay speak, even after his first stroke hindered his speech, he would sweep the audience to its feet with the eloquence of his thoughts and insights.

It’s those words and thought patterns, but also his fundamental humanity, compassion, and humility that I will miss so much. With Clay’s passing on Jan. 23, the world lost a luminary who leaves behind a treasure trove of writings, recordings, and influential relationships that will inspire innovators and thinkers in all fields for generations to come.

Clay was a master of using analogies from distant, seemingly unrelated fields to distill complicated problems to their essence and see solutions that others could not envision. He thought through diagrams and stories, which enabled him to develop a set of broadly generalizable theories that held explanatory power across different industries. He could tackle such seemingly unrelated challenges as a company’s growth, financial investing, education, health care, global prosperity, green energy, and more, because, from his vantage point, he had seen some of the very same problems elsewhere before.

As he worked across fields, rather than assume that inconvenient facts or observations were wrong, Clay saw anomalies to his theories not as problems or “statistical noise,” but as opportunities to refine and improve them — or correct how he had applied them. It’s why he had a sign outside his office that said “Anomalies Wanted.”

Clay of course had flaws, as all individuals do — and as with many individuals, those flaws were often endearing parts of his personality. Modest to the point of not interjecting a thought sometimes, he could allow misunderstandings to linger. When he told you that an idea you expressed was “interesting,” he was occasionally being genuine, but more often he was acting as a patient coach, helping you to discover where you were missing something.

He was the consummate Socratic-style professor — as the Harvard Business School teaches its faculty to be — seeking not to provide answers, but instead to ask questions to help people learn how to think, not what to think. He avoided conflict. Only rarely would someone, in his opinion, so cross the bounds of fairness or intellectual honesty that they deserved a rebuke, in which case few could be as withering and pointed in their criticisms. But for the most part, he met criticism with kindness, challenges as opportunities, and interactions as chances to inspire and praise.