Hull will spend Christmas in the bottom three after failing to win for a 10th straight game as Ki Sung-yueng's fortuitous 15th-minute goal settled proceedings at the KC Stadium.
Bruce was without several key players, with the likes of Mohamed Diame and Michael Dawson injured, while Tom Huddlestone sat out through suspension.
While Bruce was left to bemoan those omissions, he conceded that the team simply did not perform well enough to end their slump.
"I wouldn't blame it [the defeat] on luck," he said. "The second half in particular, I wouldn't say it was for the lack of effort, but the longer it went on the worse we got.
"There was nothing in it in the first half, the goal was something which we require at the moment to change us round a bit, but today it just highlighted for me the need for the big players.
"I don't want to make excuses, and we certainly need to be better than we were in the second half, but it was crying out for some of the big players who were unfortunately suspended or injured.
"When you're up against it you seem to pick up injuries and suspensions. You have to deal with it and we haven't dealt with it that well.
"It's a lack of confidence. I mean you look back to October when we beat [Crystal] Palace, we go to Arsenal [and draw], drew with Liverpool. Then November and December comes and we've had an awful run there's no escaping that.
"When you're in a run like that confidence plays a part. When you're in a run like that you need your best players to perform and there were too many today who underperformed we have to be honest about that.
"We've had a wonderful two and half years, we've now had a terrible eight weeks and we have to see it through."
Despite Hull's disappointing form, Bruce remains confident that his 19th-placed side can reverse their fortunes and move out of the Premier League relegation zone.
"There's still a long way to go, we have games against teams in and around us and you dust yourself down and go again," he added.
"You can't feel sorry for yourself in this league, it's an unforgiving league, you have to stay with it. I'm sure we'll turn it around."
