Thibaut Courtois has hailed Antonio Conte's role in turning Chelsea from also-rans to title contenders in 2016-17.
Chelsea were well off the pace last term and had to settle for 10th place in the Premier League table in May, but they appear to be well on their way to the title this season.
Conte's side sit atop of the table with 59 points from 24 games, holding a nine-point lead over second-placed Tottenham, and Courtois feels much of their resurgence is down to the Italian's arrival.
"It is good if you have a manager who is demanding a lot," the goalkeeper told Sky Sports.
"You have to be at your top every week, and that is what makes you champions.
"If you have a manager who is not demanding then sometimes you relax and you lose games."
Courtois has been a key figure for Chelsea this season, but he is not satisfied with his own performances and is determined to keep improving.
"I want to improve myself to reach a higher level," he added.
"I think I am on a very good level, but I know that I can improve myself. I think in everything you can improve.
"Everything you can improve every day and search for perfection and that is what I will try to do.
"When I was in Belgium, I played a lot of balls short. At Atletico Madrid, the trainer preferred only long balls, so you forget to play short a little. So maybe that might be the biggest point of improvement."