Teaching is an interactive process. We look around us, identify certain elements, build lessons around them, explore further and expand our knowledge. If there is a difference of understanding level or information(knowledge) level, one can step back, review older lessons , revise vigorously and catch up with the expected level.
Both teaching and learning can be great fun, if both the parties are willing to share. We all have many things to share and sometimes in this vast reservoir, certain things are eclipsed. So one should not be afraid of learning. There is no one who cannot learn . All that is required is willingness and perseverance.