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Neil Harris had been expecting a stern test of Cardiff's credentials at Brentford and admitted a poor opening hour cost his side.
The Bluebirds slipped to a 2-1 defeat as goals from Bryan Mbeumo and Ollie Watkins had given Brentford a deserved lead.
Cardiff launched a fightback when Marlon Pack's piledriver made it 2-1 on the hour, but they could not find an equaliser.
Harris, who suffered his first defeat in five matches since taking charge, said: "We can't give teams a head start or give them a foothold or you will get punished against good players.
"I knew I'd find out more about my players tonight because Brentford are one of the best home sides in the division at a tight ground, a proper old-fashioned ground.
"They can play, but this season they can go direct as well. There has been a softness about us, so I knew I would find out a lot about my lads tonight."
He added: "We didn't deserve anything for more than an hour, but the last half hour we were on the front foot, aggressive, mixing play from going direct and being able to pass the ball as well.
"Sometimes it's easy to do that when you're chasing but you have to do it from the start.
"We played some good stuff for an hour but some poor stuff too. It was the first time I've had to raise my voice at the club."
Harris is expecting a reaction against Leeds at Elland Road on Saturday and knows he will not need a repeat of his Griffin Park dressing room blast.
"I don't doubt a reaction because it's Elland Road and it's Leeds United. I've told the boys 'don't feel sorry, go again'. Ten points from 15 is still a lovely return, but I don't like getting beat."
Brentford head coach Thomas Frank hailed his side's determination to put their bodies on the line, but felt they made it hard for themselves.
"The first 30 minutes was the type of football we want to see here, moving the ball quickly, and dynamic," he said.
"We said at half-time that we needed to go for the second goal and kill the game, but when they scored I didn't like it.
"I want us to be cool, make more passes and don't stress, but we weren't. Despite that, I need to praise my players for digging in and putting bodies on the line. We showed massive desire."
Frank was disappointed with his side's attitude for a 15-minute spell after Cardiff pulled one back and added: "Maybe there was a little complacency and one or two were too slow to get into their defensive shape, but we will learn from it. It was a big and well-deserved win, but we made it too exciting."
Cardiff's aerial bombardment would have tested the Bees last season, but Frank feels they are a different side now.
"Now we are a good side from set pieces, one of the best. But we are also a side that can bounce back from defeat. All the best teams bounce back," Frank said.
