Falling off a cliff has become a favoured metaphor for business reporters regarding economic confidence in these turbulent financial times, but it could scarcely be more apt than in the case of Roy Keane and Sunderland.

Forty days ago Keane organised Sunderland's first win over Newcastle United on Wearside for 28 years. Sunderland were unbeaten in three matches, sat ninth in the table and local optimists were staring at the green fields of Europe. Then Keane and the club looked away. Sunderland has not been the same place since.

In the following five weeks Sunderland played seven games and lost six. Four of those games were at the Stadium of Light and they were all lost. Something happened in those precious moments after the Newcastle victory. Something was lost.

While concentration was focused upon the crowd trouble between rival fans, close to the centre circle Sunderland players such as Djibril Cissé and Pascal Chimbonda could be seen shirtless and celebrating. Their joy was understandable, this was a historic, euphoric afternoon for the club.

Add it to the victory at White Hart Lane in August – Sunderland's first there for 30 years – and to Premier League survival in May, when the yo-yo existence of previous seasons was ended, and there was just cause for jubilation. In the hours prior to Newcastle's arrival at the stadium, Keane had met three of the brightest youth footballers in Britain and their parents. There was a sense of progress and structure that had been lacking at the club pre-Keane.

Four days later Sunderland lost at Stoke. Bar Chimbonda, it was the same XI. But a different team. "Typical Sunderland," Keane said. He then delivered one of those fascinating deconstructions for which his weekly press conferences became known. Except this time Keane deconstructed his players – and in a portent of last Saturday, himself.

"I guarantee," Keane began, "that if I was a neutral, sat at home drinking my cup of tea and waiting for the results to come through, I'd be thinking: 'Stoke away, this is a good reflection of how far Sunderland have come.' Then, boom! Typical. That's what I'd be thinking of other teams. Typical. They win the derby match, then go down to Stoke and think they just have to turn up to win.

"But that's maybe why these footballers are at Sunderland or at other clubs that might be classed as mid-table or bottom half," he added. "There is an element of flaw in them. Some players let themselves and their team-mates down. It won't be tolerated."

This was when Keane said that he would be prepared to substitute players after five minutes. He talked about the "bravery" of Jose Mourinho's substitutions and of Brian Clough and Sir Alex Ferguson.

"They were brave managers, that's why they won titles and European Cups. They weren't average managers. My performance the other night was below average. And I don't want to be average."

It feels plausible that Keane viewed players dancing after beating Newcastle as a celebration of mediocrity and that his opinion was expressed directly or indirectly with that hatchet stare of his. "I will certainly be making changes for Chelsea," he said after Stoke.

Sure enough, at Chelsea three days later, Keane made changes. Out went Cissé, for whom Sunderland have paid Marseilles £2m for a season's loan; in came Martyn Waghorn, 18. Waghorn had played for the first team four times previously. At half time he was withdrawn, with the score 3-0 to Chelsea.

Steed Malbranque was removed too. On went Jordan Henderson, 18. By the 53rd minute the score was 5-0. Keane was sent to the stands, raging against the referee Martin Atkinson. Some people portray Keane as fearless, but this was reckless.

The wider football world may have continued to dwell on Keane's dramatic personality, but Ellis Short, the new leading shareholder at Sunderland, is understood to have been at Stamford Bridge, and he may not have.

The Sunderland dressing room and the fans started to dwell on his inconsistency. In that Monday's Sunderland Echo, the "Echo Jury" panel of contributors offered this sample of opinion: "How dare he experiment with our club by starting with youth players?" asked one. "If Roy Keane had let the supporters know on Friday about his team and the plans to effectively forfeit the game, I for one wouldn't have forked out £48 on a ticket," declared another. "Yet again we had outrageous decisions by Keane," said a third. "To start with Waghorn instead of Cissé and to play 4-4-2 against Chelsea away from home was completely mad."

Familiarity was beginning to breed discontent. When the players saw Keane give considered interviews to Match of the Day after such defeats, they knew it was not the manager they saw moments earlier. To an extent that must be true of all managers, but Keane's line on day one about being "an actor" in his playing time at Manchester United felt relevant.

After Sunderland's 3-0 defeat at Luton Town in the League Cup last season, Keane addressed that idea again: "Fake it to make it, as they say," he said. He was furious about the display but was smiling through.

That is what managers do. But Keane could not keep it up. The eccentricity of Clough beguiled Keane but it was an unpredictable pattern of behaviour that rattled Sunderland's squad. Defeats against Portsmouth, Blackburn in the Carling Cup, West Ham and Bolton followed. There was bad luck – Sunderland hit the woodwork in each of those matches – but players began to freeze.

Keane is not stupid, he must have recognised the effect his personality was having. But if he did not see, who at Sunderland did but did not tell him? If they did, did he listen?

It is hard not to reach a conclusion that the absence of criticism, friendly or otherwise, isolated Keane as a man, never mind as a manager. A prevailing view long before his bearded November, was that Keane is "weird". If people at Sunderland and at United are truthful, it is a word used frequently about Roy Keane.

£70m well spent? The best and worst of Keane's 33 signings for Sunderland

"I wouldn't trust them [TV pundits] to walk my dog. There are ex-players and ex-referees being given airtime who I wouldn't listen to in a pub."

Money well spent

Kenwyne Jones (£6m, So'ton)

Steed Malbranque (£6m, Tottenham)

Kieron Richardson (£5.5m,

Manchester United)

Andy Reid (£4m, Charlton)

Martin Fulop (£500,000, Fulham)

Jonny Evans (loan, Manchester U)

Jury's still out

Craig Gordon (£9m, Hearts)

Anton Ferdinand (£8m, West Ham United)

Michael Chopra (£5m, Cardiff City)

George McCartney (£4.5m, West Ham United)

Teemu Tainio (£4m, Tottenham)

Danny Higginbotham (£2.5m, Stoke)

Phil Bardsley (£2m, Manchester United)

Carlos Edwards (£1.4m, Luton Town)

Ross Wallace (£1m, Celtic)

Dwight Yorke (£200,000, Sydney)

Liam Miller (Free, ManchesterUnited)

Djibril Cissé (£2m loan, Marseilles)

Can I have my money back, please?

Pascal Chimbonda (£6m, Tottenham Hotspur)

El Hadji Diouf (£2.5m, Bolton Wanderers)

Greg Halford (£2.5m, Reading)

Paul McShane (£2.5m, West Bromwich Albion)

Rade Prica (£2m, Aalborg)

Anthony Stokes (£2m, Arsenal)

Russell Anderson (£1m, Aberdeen)