Gary Barlow has warned this year's X Factor finalists that talent is not enough and they will have to be able to "thrive" on pressure if they want to win the show.
The Take That star, who made his debut as a judge on the ITV1 talent show last year, said it was "hard work".
He said: "One thing I noticed about last year is that some of the acts take to being in the X Factor environment like ducks to water and they just thrive on it. Every week they come back better and better, whilst there are others that just get worse each week, taking the criticism badly and finding it hard to move forward."
The singer said most of the work goes unseen by the audience who tune in to watch the performances.
He said: "The performance on a Saturday night is the gift after a week of hard work: 'You've done all this work and here's your prize - you get to go on stage and perform'.
"The rest of it is all hard work - interviews, being filmed, working out your song, practising your song and working out how you will translate it to the audience.
"I think a lot of them get a shock. They all arrive thinking they only have to work on a Saturday night so it's a sharp wake-up call when it's not."
Fellow judge Louis Walsh, who has been with the show since it began, admitted he wished he had stepped into Simon Cowell's shoes to lead the judging panel instead of Barlow.
The Irishman said: "I've never have any regrets, although I do wish I'd taken that Head Judge mug from Gary. It is rightly mine."
This year's final will be in Manchester for the first time.