“If you want to train dragons, you have to know dragons” (From: How to train your dragon). Lucky for me, I train people, not dragons. But I believe that the analogy still stands:
If you want to train people, you have to know people.
You need to know how to help them find their own strengths,
you need to be attentive to their needs
and you need to find the fine balance between giving from your knowledge and letting them discover and experience by themselves. Over 25 years