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.