Teaching reveals gaps in understanding that knowing alone can hide.

Knowing something and being able to explain it are different skills, and the gap between them is where your real understanding gets revealed. You reach for the explanation and find a place where you have only ever had a feel for it, never a reason. That discovery is uncomfortable and it is the fastest way to improve.

Explain something you consider yourself good at to someone who knows nothing about it. Note every point where you had to wave your hands. Those are your actual gaps.