Borussia Dortmund conceded twice in the final 11 minutes, including an 87th-minute winner, away to Hoffenheim on Friday.
Lucien Favre vented his frustration after Borussia Dortmund suffered another collapse as their Bundesliga title hopes were dealt a blow.
Andrej Kramaric's 87th-minute goal completed a late comeback for hosts Hoffenheim, who stunned stuttering Dortmund 2-1 on Friday.
Dortmund played out a thrilling 3-3 draw with Bundesliga leaders RB Leipzig on Tuesday after squandering a 2-0 first-half lead.
Favre's Dortmund – fourth in the standings and four points off the pace – looked set to bounce back in their final match of 2019 thanks to Mario Gotze's 17th-minute opener.
But Dortmund came unstuck again as Sargis Adamyan equalised in the 79th minute before Hoffenheim star Kramaric struck with three minutes of normal time remaining.
"We dominated the game," Dortmund head coach Favre told reporters. "We were leading 1-0 and had more possession. We played too complicated and lost too many balls. But we had clear scoring chances.
"In the second half we can make it 2-0, 3-0, within five minutes. But we don't make it, we miss big scoring chances. I just saw another situation where we could have crossed and two players from Dortmund were completely free. The goal is empty, but we can't handle it. I have to say, that's stupid.
"You lead 1-0, everyone is a bit tired and everything is possible. When they [Hoffenheim] made the 1:1, it was hard to accept. But we have to get at least one point at the end.
"Unfortunately we didn't manage that and that's a great pity. When I imagine how many points we lost stupidly. That costs us a lot. But congratulations to my colleague [Alfred Schreuder]."
Dortmund star Julian Brandt added: "We couldn't manage to score the second goal. We lacked determination, conviction and concentration. It was an ugly result."