The striker told Champions magazine: "Rafa has taught me to demand a lot of myself daily, not to relax. When you are in a team where things are going mostly well, players tend to relax.
"But you must always push yourself and never become complacent, try to do your best every single day. At a club like Liverpool, you can't sit back after scoring 20-odd goals and say, 'Well, that's it'.
"After you score 20, Benitez is on at you during the next training session and stays on top of you all day, all week. He tells you to go off on your own and do new exercises.
"There are days when you think, 'My God, this guy does not let you breathe'. At times like that you don't realise that all he wants is for you to improve.
"I want to progress in life, not relax, not be complacent. And you need someone close to you telling you to keep at it. It is impossible to do it otherwise.
"We don't always fancy having someone like that so close. But in the long term, I'm sure everybody will thank him for it."