Manchester United manager Sir Alex Ferguson believes Sunderland fans lost faith with Steve Bruce partly because of his Newcastle roots.
Bruce, born close to Sunderland's great rivals, lost his job on Wednesday.
And Ferguson said: "Fans just don't have patience any longer, just see what happened to Steve Bruce in the North East where being a Geordie didn't help.
"In that part of the world they are so passionate and committed to their team."
Bruce, born in the North East town of Corbridge, was abused by sections of the Sunderland support at the Stadium of Light after they lost against Wigan in his last game in charge, a result that left them stuck on 11 points, only two above the relegation zone.
And Ferguson argued that Bruce's sacking provided evidence that, in many cases, supporters do not give managers enough time.
He said: "I think Brucie has suffered because of that but that's the kind of supporters we have these days - no patience.
"He rebuilt a whole team and that requires a bit of patience from everyone, including Steve. I think Steve was realising that himself that he was going to have to wait.
"I think losing to Newcastle earlier on in the season didn't help him either because of the way they are in that part of the world but he will be back. In general his managerial record is very good."
But for all his sympathy for Bruce - a man who spent nine years in his squad at Old Trafford - Ferguson suggested that Martin O'Neill would make a positive impact if, as expected, he is named as the new manager.
"Martin has a very good track record," Ferguson said.
"The job he did at Villa Park was excellent, he did a great job at Celtic, he won the League Cup with Leicester so Martin has got the experience and track record to do well.
"If that's the job he's going to, I'm sure he will do well."