Throughout the series, we've seen Champions and E4 Members meet Ash and the gang and throughout a region have a lesson that they repeat almost to the point of wearing it down.
My question is which of these trainers taught the most valuable lesson to Ash and his friends (or rivals in some cases)?
Cynthia seemed to talk about the importance of friendship and how every encounter one being makes with another is no accident but something that will help them grow in some way.
Alder kind of branches off from her lesson and saying how it is important for people and Pokemon to enjoy life and though it is important to have goals you should never be all work and no play.
Drake (Hoenn) really taught Ash that overconfidence if both a distraction and dangerous because it causes a trainer to make mistakes that they usually wouldn't make.
Bertha talked about how a trainer should pay attention to everything on and off the battlefield. It was all about the power of observation.
Flint was all about believing in yourself and your Pokemon while also using defensive tactics to strengthen his Pokemon's skills.
Lucian talked to Dawn about teamwork between trainer and Pokemon.
Steven Stone was someone of a natural/wildlife preserver I mean he was only in one episode so that's not a lot to go on.
Wallace was about bringing out the power and beauty of a Pokemon but remembered that play time is effective in Pokemon and trainer bonding.