The Reds conceded a 94th-minute winner, having led 1-0 and 2-1, and are now six points adrift of safety at the bottom of the Championship.
Head coach Struber said: “I think the performance, especially in the second half, was very good. We created good chances and took the lead then, after the equaliser, we fell into the old mindset. It is normal after the equaliser that we must be cool in our game.
“We created a good game but, in the end, we have to play our game for 90 minutes and concentrate for the whole game. That is what we need to learn.
“It’s very hard at the moment and I feel a pain in my head. It’s very difficult for me, my staff and especially my players. But we are very close and, in the next away games, I hope we can win. We are 98 per cent there.”
The Reds played some impressive football and had chances to increase their lead at 2-1 but were defeated by a direct home side.
Struber said: “We had good positioning, good courage and played good football. If we play like Cardiff with the long ball, we had no chance. But we had a chance when we played quick football. This was what we did in the first 20 minutes of the second half but not after the equaliser. I am very disappointed because we were so close.
“We must learn to grow up and I hope the boys get better from this experience and learn from the game. I hope for good results away and home.”
Struber said he did not think Barnsley should have had a penalty for a foul on Conor Chaplin at 2-1. He thanked the away supporters and is hoping to repay them in the home games against Reading on Wednesday and QPR on Saturday.
“Our fans always do a top job. It’s a long way from Barnsley to Cardiff and so many supported us. I hope they support us for the next games like that again. It was a great support and it helps us.
“In the two home games we need a good performance with the right character and attitude and, in the end, we will have the benefit. I hope, after those two games, we have the necessary points.”
Clarke Oduor, who made his debut in stoppage time at 2-2, added: “It was great to finally get out there. It was bittersweet because we didn’t get a point or a win out of the game.
“I think the results will come with the next two games being at home. We can all rally together and get something out of those games.”