Defender Liam Rosenior said Albion's defeat to Bournemouth on Friday was a harsh lesson for the team.
Rosenior felt it also showed the step-up in class from the Championship last season after goals from Andrew Surman and Jermain Defoe took the Cherries to victory.
Solly March had given Albion the lead and Rosenior said: "I thought we were outstanding for three quarters of the game. It's a harsh lesson for us today that any lapses in concentration, the smallest of mistakes, can lead to goals.
"Fair play to them, it was two real bits of quality that won them the game. Saying that, I can't remember them having another shot on goal.
"That performance was going back to our Championship days away from home when we saw games out. There's things we can take, we can take lessons from it and we can also a lot of positives.
"It was a good performance. The time they scored their first goal was when we were most in control but that comes down to concentration. We showed a lot of good things today and that's why we've had a good consistent couple of years. Everybody is willing to work for each other and on top of that we've got good footballers.
"We played some excellent football at times tonight. You don't want to say it's unfortunate we've lost the game but we need to learn lessons very quickly that we can't make small mistakes."
Rosenior added concentration levels need to remain high throughout games and said: "You have to make sure you keep your back door shut and make sure everyone is focused and concentrated.
"First half in terms of concentration and discipline, we were outstanding and in the second half we started to play our football when the game opened up.
"We had a few chances before the goal. I don't know about the stats but we had probably the better chances than they did over the game but they took their chances and that's what happens at this level. Two chances, two goals and that doesn't happen in the Championship.
“In terms of this level, you can't switch off for any moment in the game, because people like Jermaine Defoe are going to punish you and we got punished."
Reflecting on the opening five games, with Albion on four points, Rosenior said: "We could have got more points for sure but in saying that the lads who haven't played at his level before are learning really quickly what it's all about.
"I maintain that the difference between the top of the Championship and bottom half of the Premier League isn't as big as what people make it out to be and we've got a lot of cause for optimism moving forward."