Chelsea boss Frank Lampard was frustrated with their errors for Saturday's 3-3 draw at West Brom.
Thiago Silva made a costly error which allowed Callum Robinson to get his second goal of the night, having already profited from Marcos Alonso's sloppy header to open the scoring, while the Spaniard was also at fault for Kyle Bartley's close-range finish which put the Baggies 3-0 up before half-time.
Mason Mount and half-time substitute Callum Hudson-Odoi gave the Blues hope with strikes after the break before Tammy Abraham's 93rd minute equaliser earned a draw, but Lampard was still far from pleased.
"You can do as many meetings as you want -- if you're going to make those mistakes, you're going to give yourself a mountain to climb," said Lampard, unable to hide his disappointment at two points dropped to their newly-promoted opponents.
"We created two or three great chances in the first half, I felt we would create more, the only other problem at 3-0 was West Brom were going to protect their lead more," he added.
"It is a big lesson for us. We will get a lot better. We're still finding our way with new players and a lack of pre-season. Today is part of the process of getting better."
The draw leaves Chelsea in sixth place on four points from three games, with three of the five teams above them having a match in hand.
"We have two big games coming up against Tottenham (in the League Cup fourth round) and Crystal Palace. I expect to see an improvement in our performances," Lampard said, before adding a note of caution about his side's conditioning.
"In terms of team fitness, it won't be until after the international break (in October) that I expect to see us up to our real level, especially in terms of on the ball, because we haven't had time to work on that yet," he added.
