This uncovers in your own mind where the soft spots are in our understanding. Head said that puts a premium on questions that some people consider naive.
Undergraduates are unencumbered and some of their best questions are the so-called naive ones.
Sometimes at the graduate level, students are intimidated to ask simple questions because they are worried that they should know the answers. Yet some of the simplest questions are the most elegant. These are the questions people who are deep into their field have forgotten to ask. This enthusiasm and excitement about new ideas is infectious, and keeps you young. The direct interaction, the ability to have students experience what the research endeavor is all about, allows you to harness that energy, and it's wonderful for them.