Chelsea had produced plenty of encouraging football at Parc des Princes on Wednesday night and were still competing strongly late in the game. However, the contest slipped away during the final 15 minutes as PSG struck three times to seal a heavy win.
Rosenior pointed to a costly defensive error that allowed the French champions to move ahead at 3–2 before two late goals finished the job. The Chelsea head coach said the team's inability to stay calm in difficult moments remained a key issue.
"We've spoken since my first day about reacting positively and staying calm in pressure moments, and that's why it's on me," Rosenior said after the match.
"I need us to maintain our calm in the moment we have setbacks. A lot of what we did – the intensity of our press, some of our football, the chances we created – was outstanding.
"But if we don't overcome this hurdle we won't reach our potential. It's my job to find the answer to it."
Despite the frustrating finish, Rosenior believed the team were close to becoming a top side if they could improve their mentality during difficult spells.
"We are very close to being an outstanding team," he added. "But we have to overcome this hurdle to make sure that happens."
Rosenior also urged his squad to stick together ahead of their next challenge. Chelsea return to Premier League action against Newcastle United at Stamford Bridge on Saturday, and the coach expects a strong response.
"This is a big test of our character," Rosenior said. "We have a huge game in two days against Newcastle. I want to see a real reaction and resilience in the next match."