Mentored a junior for the first time last month and realized how much I actually know only when I had to explain it out loud

Got asked to pair with a new hire on their first ticket, assumed I'd mostly be figuring things out alongside them. Instead kept catching myself explaining decisions I make automatically now, without ever really examining why, tradeoffs I'd internalized without noticing. They asked a question about a pattern in our codebase I couldn't fully answer, went and actually researched it properly for the first time in two years. Teaching exposed both how much I know and how much I'd stopped questioning.