The Tykes seemed to control much of the game but it was teenager Jude Bellingham who forced the only goal of the game with 14 minutes remaining, dispossessing Jordan Williams before laying the ball off to Scott Hogan, who fired into the top corner.
Struber said: "It was a very tough game and in the end, we got zero points. It's a very difficult situation for me, my staff and the whole team.
"The performance was not enough to win this game, we need full focus in every action.
"I've spoken before about mistakes – we have to learn from these mistakes. In every game we have a blackout and today it happened again.
"We're not learning from mistakes, which is not easy for us. It was not only the mistake, but we didn't create enough in the attack...our positioning, our forward runs – and we didn't have that precision in the last pass.
He continued: "We had good moments which came more from long-range shots. We had control on and off the ball – but we still lost. This is the reality, the feeling right now is really bad.
"On the ball we had good positioning, but the precision of our final pass was not enough to score goals. Our opponent was very good in their defending, they were very organised.
"We have young players with a lot of talent who need time, but with our challenge, we have no time. It's a very frustrating position for us but we have to fight."
Birmingham head coach Pep Clotet expressed how pleased he was with his side's mentality.
Clotet said: "We're very pleased with the three points because in the end that's what the goal is, every game.
"It was a difficult game for both sides, who were affected by the conditions.
"We knew the conditions before and we kept that in mind with the way we played so that we would come out on top.
"I thought before the game (it) would be decided by quality in the box and by little mistakes.
"We tried to minimise mistakes and rely a lot on our defensive side of the team, which was very good.
"We knew the chances would end up coming and whoever scored the first goal would have a very good chance of winning.
"Here at Birmingham we never say never, we work hard and never give up and that showed with today's goal.
"We go in with a mentality to get as many points as we can from every game. We stick to game-by-game, that's what we're doing.
"If the game doesn't turn to our side, we need to make sure we don't lose and we did that tonight."