Alexis Charles Henri Clérel, Viscount de Tocqueville was a French diplomat, political scientist, and historian. He was best known for his works Democracy in America and The Old Regime and the Revolution. source
They taught us because they wanted to pass the knowledge on and educate young musicians. It was not because they had to teach because they failed as musicians. There is a huge difference in the reasons why someone is teaching and what they can offer and what they cannot offer.