Mourinho, twice a Champions League-winning boss, has faith in his side's ability to respond in adversity and upset the odds after a 3-1 quarter-final first-leg loss in Paris.
"Reasons to believe? I think the reasons are not important," Mourinho said.
"I believe and my players believe. That's the most important thing.
"I think if Paris tomorrow is knocked out it will be a big disappointment for them; if tomorrow we are knocked out it's something that, in this moment, lots of people are expecting.
"We have to enjoy the risk of the situation. At 9.30 (on Tuesday evening) we can be out and we know that we have this risk. But at 7.45 we have chances to be in the semi-final.
"We have to be at 7.45 with a smile on our faces, go in, play, give everything. At 9.30, let's see what happens. But at 7.45 we believe that we can do it.
"I think we are going to win, really. In the end of the two legs, I think we are going to score more goals than them.
"In this moment it's 3-1, I think in the end it can be 4-3 or 5-4.
"If I don't think that way I don't go tomorrow. And I go and I'm happy to go."
Mourinho insists Chelsea were more culpable than PSG were good in the loss at Parc des Princes last Wednesday.
"In Paris we would expect Paris to play very well to control the game, to have the ball, to be very dangerous," Mourinho added.
"We were dangerous to ourselves, because we scored half of the first goal, we scored the second goal and we scored the third goal.
"Plus our goal, we scored three and a half goals in that match. It was not Paris that played very well."
PSG have lost just once by two clear goals in their last 110 fixtures, while only two sides in Champions League history have overturned two-goal deficits, with Chelsea involved in both contests.
In 2000, Barcelona advanced at Chelsea's expense, but in 2012 Chelsea overcame Napoli after extra-time in the last 16, en route to winning the European Cup.
For Mourinho, only one statistic matters.
"The only thing I know is that if we don't score a minimum of two goals we have no chance," Mourinho said.
"If they score one, we have to score three, at least. If they score two, we have to score five.
"This is the only thing I know. The basic thing of the numbers, the basic mathematics.
"How the game is going to be? I don't know really.
"They can say they come to attack and maybe they don't cross the midfield line.
"Maybe they say they come to defend and they find spaces and score goals. We don't know."
Mourinho could be prepared to risk striker Samuel Eto'o, who has scored all 11 of his goals this season at Stamford Bridge but has missed the last three matches with a hamstring injury.
"I'm not sure he plays the second game," Mourinho said.
"Fit, fit, I don't think he is. But play tomorrow, maybe."
Chelsea, who beat Stoke on Saturday after three losses in the previous five games, must replicate the Napoli result to advance to the semi-finals for the seventh time in 11 years.
A few months after the Napoli comeback, the 2012 season culminated in success in Munich, reminders of which are everywhere.
PSG forwards Edinson Cavani and Ezequiel Lavezzi were in the Napoli side beaten by the Blues, while Tuesday's referee Pedro Proenca was also the man in the middle against Bayern Munich.
Mourinho called on the home support to contribute to another memorable occasion.
"If they (the fans) can push us a little, that push is welcome," Mourinho said.
"But everything starts with us. And I think if we can show that we can do it, I think they will come with us."
Proenca leads a team of Portuguese officials, something which his compatriot Mourinho believes is incidental.
"The referee is obviously one of the best," Mourinho said.
"The fact that he's Portuguese and you mention it surprises me, because I played a Champions League semi-final against Liverpool with a Spanish manager (Rafael Benitez), I had a Spanish referee.
"I played last year against Man City with an Italian referee and an Italian manager (Roberto Mancini). That's European football."
There is another Portuguese connection, with this season's final in Lisbon on May 24.
"I want to try always to do it, for me, for my club, for my players, for our supporters," Mourinho said.
"The fact it's in Lisbon doesn't play a role in my motivation."