Chelsea lost to Basle in the opening round of matches and are bidding to make amends at the National Arena in the Romanian capital.
Chelsea have been here before, with Raul Rusescu's first-half penalty earning Steaua a memorable win in the Europa League last 16.
"It's good for me," he said. "They lost, they know why they lost, they know it's not easy.
"Last season maybe was a bit of a surprise and this season they know they are going to play against a good team."
Mourinho is without playmaker Eden Hazard (ankle) and his fellow Belgian Kevin de Bruyne, who was left at home after failing to impress his manager.
The Portuguese was frustrated to once again be asked about a player not involved due to his non-selection, just as he was with Juan Mata in the early weeks of the season.
Mata will play on Tuesday night, Mourinho has said.
Another probable starter is midfielder Frank Lampard, who insists there will be no complacency on this occasion, with Chelsea knowing what to expect after experiencing a team roared on by a raucous crowd in March.
"You can never underestimate any team in the Champions League," Lampard said. "In the first game we didn't perform well, we lost. That's what happens.
"(But) we've got five games now to go, five games to put that right. That's a lot.
"We don't expect an easy game. We're lucky to have played Steaua Bucharest last season so we're fully aware of the good team they are. Last year we started slowly and we lost the game in the first half.
"Considering the position we're in now - we need a result tomorrow - we have to start the game at a top level.
"If we turn up, think 'we're Chelsea, we're going to come and play and win the game easily', that's not going to happen.
"It's down to us."
When the sides last met Rafael Benitez was in charge, overturning the first-leg deficit in London en route to lifting the Europa League trophy.
Now it is twice European Cup-winning boss Mourinho in the Blues' dugout and the Champions League.
"We've met Chelsea, but this time is different," Steaua boss Laurentiu Reghecampf said.
"Another coach, the best in the world, and another competition. It will be something else.
"I'm sure Chelsea comes Bucharest to win. For them it is very important to qualify from this group.
"It will be more difficult for us, but do not think Chelsea is superior.
"I'm sure our guys will be more determined and focused.
"Together we are a team that can handle these games. We'll try show our collective strength, give them problems."
Reghecampf has vowed his side will make amends for their 3-0 loss at Schalke in their first home game in the competition for five years.
"We will play a lot better than we did in Germany, against Schalke," he told reporters.
"We want to leave little space, to be very well organised and try to show our offensive qualities."
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