Fabian Hurzeler said [Albion](https://www.theargus.co.uk/sport/albion/?ref=au) missed a chance to make Carabao Cup progress.
He saw his side go down 2-0 to Arsenal in the fourth round after letting first-half openings pass them by.
Hurzeler said:“When we take all the chances, we are in the next round.
“It is about scoring and defending and we were not able to score or defend the most important actions.
“The goal from Arsenal changed the game and it is not easy to score goals here as we all know.
“Small margins. Defending the edge of the box, defending the give and go, we can do it better.
“Every goal gives you confidence.
“I think also in the second half we had not an amount of chances but good possibilities to score.
“We will keep working hard and give the players the right support.”
Charalampos Kostoulas had a bright first half in his longest outing yet since coming to England from Olympiacos.
But he was replaced at half-time.
Hurzeler said: “He played very well. It was physical reason why we took him out.”
Confirming that not an injury, he added: “He runs a lot. He needs time to adapt to intensity of the Premier League, ne heeds to adapt to the demands.”
Arsenal boss Mikel Arteta said: “We were struggling in the first half. I expected that when you make ten changes and you have players that have never played before and some of them haven’t played much this season.
“You have to gamble. But I was ready to take that risk and in the second half, we needed to start in a different way and we certainly did that and the game shifted momentum.”