The Blues were downed 3-2 by the Premier League relegation battlers, a defeat which meant they missed the chance to moved into third.
And speaking after the game, Lampard said the result was indicative of why his team were not challenging for the title.
“It happens, it is the Premier League and if you make mistakes like we did, we dominated the game in terms of possession, but make mistakes and teams will hurt you,” said Lampard.
“I’m not happy with any of the goals. You don’t get given victories for scoring two goals, you have to be better than that.
“There were moments they counter-attacked, which we knew they would. There were details in the game which we knew but we lost because we didn’t get them right.
“It is why we are fighting for the top four, not one or two, because we don’t get things right as much as the big boys do. I am not happy with tonight but at the same time, we are two points ahead of Manchester United, who have been going great for some time.
“If you don’t get details right in big games, you’re going to drop points. I think at times we have played really well this season. As a group, we need to find more consistency.
“We have to defend the moment better. Against West Ham, you have to make recovery runs. That is the bit we got wrong.”