Neil Harris describes Millwall as 'falling short' on Saturday afternoon as Brentford ran out 2-0 winners over The Lions at Griffin Park.
Second-half goals from Sergi Canos and substitute Ollie Watkins sealed the three points for The Bees, a first victory in charge for Danish manager Thomas Frank.
The result leaves The Lions 19th in the Sky Bet Championship, one point above the relegation places.
"I thought we fell a little short in quality today, if I'm honest," the manager says.
"Yes, we are what we are - underdogs and overachievers at this level - but we're also professionals as well. We have our style of play and we know what we expect at this football club, and what I demand of the players.
"There was nothing in the game today apart from two disappointing goals we gave away, but ultimately we didn't do enough with the ball. We didn't show enough composure or quality."
Harris commends the work-rate of Frank's Brentford, and admits lapses which led to the goals after the break.
"Brentford worked extremely hard, and we completed our gameplan to frustrate them for much of the game and win the ball high up the pitch as much as we could, but when you give poor goals away, it makes life difficult for yourselves.
"The goal at the start of the second half killed us, because we came out really well from half-time before they scored. We spent nearly four minutes in their half, and then we gave the ball away cheaply outside our own box with the ball ending up in our net.
"After that, we chased the game - we tried to be more attacking but we didn't create enough chances, something we've done plenty of recently. Things like second balls - that we pride ourselves as being one of the dominant sides in the division with - weren't quite there today. You have to give credit to Brentford who worked very hard, and a lot of 50/50 balls fell their way - that's football."
The boss claims that a lot of the accuracy in decision-making was off the mark, but claims difficulty in making the right choices to create chances is not a regular problem.
"I thought our decision-making was poor. We could have played more balls forward than we did in the first half, and got caught in possession, and then in the second half we moved it forward too quickly when we could have made an extra pass or two.
"The moments we did get it right, we showed some composure, got box-to-box, and we put a couple of balls in the box. But apart from a couple of shots from Jed [Wallace] outside the area, we didn't create much in the way of clear-cut chances in the second half.
"I accept it from the group, it's not an issue. We've recently been creating 20 chances a game, but today was a frustration. We're disappointed, but the group have come a long way in the last six weeks, and we want to keep improving."
Next up for Harris' men is another crack at a first away win of the campaign, travelling to Daniel Farke's Norwich City next Saturday - whose 4-0 victory at Sheffield Wednesday sees them rise to the top of the pile.
"It's a disappointing result for us on the road in a London derby, but we certainly pick ourselves up and look forward to another tough game next week away at Norwich."