The Tigers began the day in buoyant mood having bagged four wins in their previous five games.
But Dean Marney's first half strike was enough to secure the spoils and Bruce said: "We had too many of our good players not playing as well as they should have been.
"That caused us a problem. We've got to rid ourselves of that Achilles heel and start taking something out of games in which we don't play well.
"The Championship has wrecked a few coupons today. It's a really difficult league because of the inconsistency of it.
"We didn't do enough in the first half and Burnley were comfortably the better side. If it had not been for our goalkeeper it could have been worse at half time.
"We did not pass the ball as well as we do usually and gave the ball away too much in the first half, and we didn't get the momentum going.
"We changed things for the second half because we had to do something, and we did get better and showed a bit of urgency, but we huffed and puffed a bit.
"When you analyse things, we haven't had a proper shot on target, even in the second half, so we deserved what we got. You have to give credit to Burnley because they defended very well."