The Scot insists there can be no excuses for dropping two points at home.
He said, "When you go slack you get what you deserve. When you come up against a Sam Allardyce team you know they will stay in it and take the one chance they get.
"We created a lot of chances in the first half and then in the second half it was as if we didn't want to do it again. We went slack. Every one of us made a mistake in the second half which can't happen. Credit to West Brom for the way they played the second half.
"You know they will look to frustrate you and play the game down and hit you on the counter-attack. We didn't let them do that in the first half and then they grow with confidence the longer it goes 1-0. We should be experienced enough to see it out and build on the 1-0. We should have been 2-0, 3-0, maybe 4-0 up at half time. We were dominating and it was up to us to take the chances but we also should be professional enough to win 1-0 if we have to. We will take the point and move on. We can't dwell on it but it's a huge disappointment.
"I've been in a Championship team that has come up and you want to frustrate the big teams and get that one chance you can get and that's exactly what happened. Credit to them. They were great in the second half but we need to be so much more professional. We didn't do that enough and that is frustrating."