Our Head Coach spoke to iFollow Barnsley after a 1-0 defeat at home to the Imps.
One goal was once again enough to consign the Reds to defeat in our first league meeting with the Imps since 1976.
The breakthrough was made by Daniel Mândroiu on the stroke of half-time, after a raking ball by Jack Diamond found the former who dispatched coolly into the bottom corner. Duff felt the goal was a soft one to concede from a Reds perspective.
"We concede from their only shot on target in the game - a poor goal to give away," he affirmed. "Once you give a team like that a goal or an opportunity, they just want to sit in and hit you on the counter.
"They do it well, we knew that's what they would do."
Despite a bright opening from the Reds, the 44-year-old believed that his side weren't good enough in the final third on Tuesday evening to warrant finding a way past Carl Rushworth in the Lincoln goal.
"Frustrating," he admitted. "We moved the ball, opened them up numerous times and just couldn't find the final ball.
"Whether it was a cross or a pass. It's a little bit where we're at. We've got into good areas so many times and couldn't find that little bit of quality that we've been lacking in the last couple of weeks."
Throughout the game, the Reds accumulated six corners and won multiple free-kicks from crossing areas on the pitch.
The boss was discontented with how his side utilised these opportunities during the game.
"Another frustration is that we've had corners and wide free-kicks, that's an opportunity to score a goal.
"It isn't a case of, 'the centre-forwards are missing loads of chances', it's the ball, the final ball, the final pass - it hasn't been good enough tonight."
Obviously, whilst disappointed with the result, Duff was encouraged with how the Reds used the ball against Lincoln compared to Saturday's performance against Morecambe.
The gaffer explained the elements of play he was happier with, whilst admitting the pattern of the game led his side to become more rushed in possession as the clock ticked on.
"I thought it was better than Saturday," he said. "At Morecamve, we just started taking potshots from everywhere. We didn't do that [on Tuesday], we kept it in the top-third. We tried to upgrade the chance almost, instead of just having a shot from 40 yards.
"The last 20 minutes become scrappy. The players are human beings, they're not stupid. They're desperate to get back in the game. It wasn't through a lack of effort or commitment today. Ultimately, we got undone by our lack of quality and a clinical Lincoln."