He knows more than he lets on. You can tell by the way he solves problems. He does not call himself an expert. He is uncomfortable with the label. This is Authority Anxiety. The knowledge is real. The confidence in sharing it is not.
Practical Techniques
Give the Task a Structure
Unstructured sharing scares him. “Just share what you know” goes nowhere. Give him a form. Ask him to write the three most common mistakes in his area. Ask him to review one document. Give the task a scope. He can do a task.
Tell Him Specifically What Landed
General praise does not build confidence. Specific evidence does. Say: “The way you explained the timeout issue in that session clicked for the whole team.” Or: “Three people told me your walkthrough cleared things up for them.” He can hear a fact. A fact is harder to dismiss than a compliment.
Start Small
Don’t put him in front of twenty people first. Start one-on-one. Ask him to contribute to a shared document. Run an informal session with two people who have a real problem. Each successful share makes the next one easier.
Why This Works
Authority Anxiety is not modesty. It is a real fear of being judged or found wrong. Structure removes the open-ended risk. Specific feedback gives him evidence that the sharing worked. Small starts let him build a record before the stakes go up.
Don’t Try to Change the Anxiety
Your job is to make sharing easier, not to change his personality. Create the conditions. He does the rest.