The self-proclaimed 'Special One' played down Chelsea's 2012 Champions League victory and their Europa League triumph last season, claiming the successes papered over the cracks of an inconsistent and mentally fragile team.
The Blues finished sixth in the 2011/12 season - 25 points behind champions Manchester City - and third last term, 14 points adrift of Manchester United.
Mourinho said: "If you see the position of Chelsea in the last leagues and the difference of points from Chelsea to the champions, you can imagine that even with a magic click - that I don't have - it's not easy to recover 20 points. It's more than one click.
"For a club like us it's not good to be 15, 20 points behind.
"We need to win seven matches 1-0, not win one match 7-0 and lose the other six, or lose points.
"This is the kind of mentality that you have to build. And it's much more difficult.
"I had a team of players in the best moment, potentially, of their career (in his first spell as boss).
"I needed a click to make them believe. At this moment, in terms of building a team, the task is different."
Mourinho believes the title race is open this term, but he knows his players have to improve their mental approach and become more consistent if they are to challenge for silverware.
"We need to be more consistent. I don't think we are strong enough at this moment to have that kind of run of victory, victory, victory," he added.
"We will, for sure, we will. In this moment I don't think we are.
"The players must feel and accept the responsibility to play for a big club with big ambitions, where you cannot fail, where you cannot play one good game, one bad game, win one game, lose another".