Great leaders know that every innovation begins with a problem. Instead of telling their people to “bring me solutions,” they encourage folks to be on the lookout for problems worth solving.

Legendary Stanford professor Bob McKim had a simple, standard response to any student seeking his feedback on a new project. Google X’s Astro Teller does something similar today.

Legendary Stanford professor Bob McKim used to give design students a simple assignment: keep a bug list. This was decades before computer programming gave the term the meaning it has today.

Whenever a student asked legendary Stanford Professor Bob McKim for feedback on a new design concept, he consistently gave the same response: “Show me three.” Those three words contain a remarkable depth of wisdom.