"We came out far too slowly in the first half. Coventry had a game plan and we simply didn't deal with it," Boothroyd said after the 3-1 defeat.
"The second half was different. We scored a great goal and had we nicked another I felt we could have won it, but we didn't manage to do that.
"You really have to be on your mettle in this division. You get punished for your mistakes and we need to learn that you can't play for 45 minutes or for an hour. It is a 95-minute game these days."