David Weir admits he is still hurting at the manner of Saturday's disappointing 3-1 defeat at Rotherham on Saturday.
The Blades boss says the South Yorkshire derby loss at the New York Stadium is still angering him because all three of the Millers goals were, in his opinion, avoidable.
He remarked: "It was the manner of the collapse in the second half that hurts the most; I still can't believe we just rolled over after the equaliser.
"After being comfortable in the first half, the second half was very, very disappointing. The manner of the goals makes it doubly disappointing because we were our own worst enemy.
"I think we contributed in a big way to our downfall, there's no doubt about that. The level of the goals we conceded and the level of the mistakes were very, very poor.
"It is going to be difficult to win a game of football when you commit that level of mistake."
Weir continued to outline his frustration, adding: "We were on top in the first half, but a game of football doesn't last 45 minutes, it lasts 90 minutes.
"It was the reaction to their first goal that was the worst thing about the game. We have got to be stronger than that and, obviously, that is another disappointment.
"We did well in the first half and got ourselves in a good position, but you get nothing if you capitulate like we did."