After expressing concerns about the chain of events leading to Rotherham's equaliser at New York Stadium, Chris Wilder was frustrated to see his team gift Leeds victory when the two clubs met in South Yorkshire threeÂ days ago.
Speaking after Dean Henderson's miscalculation presented Pablo Hernandez with the only goal of the game, Wilder described how the 21-year-old's blunder came on the back of a poor back pass by defender John Egan.
The United manager, who absolved Marvin Johnson of sole responsibility for Jamie Proctor's 92nd minute strike seven days earlier, said: "One mistake, I told them last week, can't become two mistakes. If someone makes a mistake, which will happen, then someone else has got to be ready to cover or dig them out.
"Everyone is going to get things wrong. No matter how hard to try and eradicate that, it's human. It's life. But what shouldn't be allowed to happen are situations were one becomes two or even three."
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With the margin for error at the top end of the Championship growing increasingly slim - only six points separate the division's leading seven teams - Wilder is aware that more careless play could have serious consequences for United's hopes of competing in the Premier League next term.
Although they are preparing for this weekend's visit to Reading in sixth place, Wilder's squad would be second, within touching distance of leaders Norwich City, had they not lost to the visitors from Elland Road and drawn with Paul Warne's side.
Johnson, aged 28, was criticised in some quarters for his part in the build-up to Proctor's effort last month.
But Wilder said: "Some people blamed him. But what I look at is what followed on from that; when experienced players should have dealt with the situation but didn't. Instead, they made poor decisionsÂ and that's what I'm talking about. That's what we've got to look at and try to cut out."