Daniel Farke refused to shy away from his true emotions after seeing Norwich City comfortably beaten at Millwall in the Sky Bet Championship on Saturday.
The Canaries conceded three times in the first half, before a Shaun Hutchinson header in the second period completed a comprehensive 4-0 win for The Lions.
Speaking to Norwich City TV, Farke said: "Our defensive behaviour in the first half was why we lost the game.
"We conceded the same goal at least two times. They were easy goals and I'm really annoyed.
"Conceding 12 goals after five games means normally it's not possible to win. We have to work on it.
"I have to either improve the players or find some other solutions. It's up to me do that and that's what I'm planning to do."
With a two-week break from domestic action for the September international fixtures, Farke knows there is much to work on.
"I'm totally annoyed and frustrated about our defensive behaviour," he added.
"I totally understand the fans' concerns. When you watch the first half, you have to be concerned.
"Making the mistakes we did, it's not posssible to win games. We have to improve.
"I'm hurt and the squad is hurt. We are angry and really sorry for the fans as that's not what we want to bring."