The Gulls beat Solihull Moors for a first win in nine, but Nicholson was unhappy with the attitude afterwards.
"We came in after beating Solihull and too many of the team looked like they'd made it," Nicholson told BBC Devon.
"You should be in on Thursday and you should be head down let's get ready to go and beat Tranmere."
He continued: "Overall it was an OK half and then one terrible bit of defending and a goal and you throw away all the good work that you've done.
"But then that comes from a will to improve, you've got to put the work in every day at training, so that those kind of mistakes stop happening."
Torquay have not beaten Tranmere since 1998, having lost the last three matches the two sides have played since Rovers were relegated to the National League in 2015.
"It's sad that Tranmere versus Torquay should be a clash of two titans in this league and we're coming here as huge underdogs," added Nicholson.
"It shouldn't be that way, our lads have got to set the standards and targets a lot higher than what they have, however they kept going and played some reasonably good football."

Borthwick, 36, left his role at the Championship side after only 43 days.
The former England captain arrived at Bristol several weeks into the season having helped Eddie Jones coach Japan.
"It's kicked us quite hard because this has been about planning and waiting for Steve to arrive," said Robinson.
Borthwick was named forwards coach with Jones' new-look England in acrimonious circumstances last week, with Bristol owner Steve Lansdown describing the Rugby Football Union as "unprofessional" in their handling of the appointment.
Robinson was forwards coach during England's World Cup-winning era under Sir Clive Woodward before taking over as England head coach himself from 2004-06.
And, while he is unimpressed by the manner of Borthwick's exit, he is certain England have made an astute appointment.
"I was delighted to have signed Steve and I certainly hoped he would be here for longer than 43 days," Robinson told BBC Radio Bristol.
"He is a quality coach and he will be a quality coach for England and I wish him all the best. I know the England team will enjoy working with him.
"I'm disappointed in the circumstance of how it's happened and why it's happened but legally I can't say too much and we have to move forward."
Robinson, who has also coached Scotland, says he will not rush into appointing a replacement and has urged his forwards to handle the responsibility of Borthwick's departure.
"It's down to the players to step up collectively over the next four months for us to achieve what we want to achieve," he said.
"We have to focus on the next couple of weeks, with tough games coming up against London Welsh and Nottingham. There is a lot to be done over the next few weeks."
Torquay United manager Kevin Nicholson says his side's attitude in training ahead of their loss to Tranmere Rovers contributed to the result.
[NEXT_CONCEPT]
Bristol director of rugby Andy Robinson says the club have been hit hard by the departure of forwards coach Steve Borthwick, who he believes will be successful with England.