Southampton striker Rickie Lambert admits the step up in quality from the Championship to the Premier League has shocked a few of the players.
Back-to-back promotions have seen the Saints rise from League One to the Premier League in just two years.
Nigel Adkins's side have struggled so far, with just one win from 11 games.
Lambert described the Premier League as ruthless and said: "We were all expecting a step up but it has shocked a few of us. It is harder."
Speaking to Football Focus, he added: "I think the main thing is that any mistake we make gets punished. It is ruthless.
"The Premier League has the best players in the world and this is where we want to be.
"We are learning very fast and have to stop making the errors and score the goals at the other end."
Lambert scored over 20 goals in each of the past three seasons for Southampton after joining from Bristol Rovers.
He is the club's top scorer this season with four goals, but has not scored since his double helped Southampton to their only win of the season - a 4-1 victory over Aston Villa on 1 September.
"I have definitely noticed the difference," said Lambert.
"Every defender is very intelligent, stronger, faster and you get less chances but you still get chances.
"You still have to be confident that when a chance comes you can put it away."
Southampton head to QPR on Saturday, with manager Adkins coming under increasing pressure to improve results.
Lambert believes the former Scunthorpe boss is the right man to turn things around.
"I definitely want him to stay," he told an earlier news conference.
"He looks at me to try and lead the team as well and I am trying obviously to help him.
"I understand he is under pressure but it is not nice, it is not his fault. It's all of our fault.
"It's little errors that are costing us at the moment but I think some of the performances this season have deserved more points than what we got."
Watch the full interview on Football Focus on Saturday at 12:15 GMT on BBC One and online.