Speaking after seeing his team concede an equaliser deep into stoppage time against Oldham Athletic, Danny Wilson was understandably frustrated.
Matt Smith poked home for the Latics with what was the last meaningful kick of the game after Nick Blackman's penalty appeared to be sending the Blades to a sixth win of the season.
In the aftermath, Wilson said: "I think it's a lesson we have to learn.
"Give Oldham credit, they have persevered, which you'd expect us to do if we were in that situation. Then they've got a break and nicked a point.
"What's more disappointing is that we've not dealt with a ball that we've dealt with throughout the game.
"We've just got flat footed. The ball's been lofted in and everyone just admired it and nobody tracked the runner.
"Despite having chances to make the points safe, we should have seen the game through at 1-0.
"We have been punished for thinking the game was over, but we will learn from this experience."
The Blades boss was critical of his team's display in the first-half, but praised their response after the break, as United extend their unbeaten start in League One to 12 matches.
"We weren't at the races, we didn't play with tempo and Oldham pressurised us on the ball.
"After half-time we upped the tempo and caused them problems thoughout."