Since I don't know Pier Gauthier (except that he was Seb's coach and friend), I googled his name. He is specialized in NLP (neuro-linguistic programmation), whatever that means. He also coaches managers, he's not only a tennis coach. He is a former tennis player (his best ranking was around #200 in the nineties). But it definitely looks to me like he works more on the mental side of the game. I hope they'll find the right balance with the technical aspects because Gael needs to improve in that regard too.