Sir Alex Ferguson believes whichever team loses out in the title race will be haunted by the missed opportunity, as he looks forward to the Manchester derby on Monday night.
Manchester United currently hold a three-point lead at the top of the Premier League but Manchester City have a superior goal difference and will climb above their rivals with a home win at the Etihad Stadium.
There will be just two games remaining for each side after Monday's game and the outcome is likely to decide the destination of the title.
The fact that it is a derby has only added to the hype and Ferguson appreciates that for supporters it could be the biggest game of their lives.
The Red Devils manager also concedes that the club finishing second will feel they have thrown away the title, with City having occupied top spot for most of the season before United opened up a seemingly insurmountable eight-point advantage just a couple of weeks ago.
"I'd agree with that," said Ferguson. "I think there will be sense of that from both parties.
"If one loses, they are going to be reflecting on what may have been.
"But then you look at the points totals that both teams are probably going to amass and you'll see that it's championship form.
"But, yes, whoever loses will be tinged with regret, simply because it's a derby thing.
"This is the derby game of all derby games. City are our nearest rivals and it makes everybody step up a notch in terms of anticipation.
"It means everything to the supporters.
"Going in to work next Tuesday morning will be the most important day of their lives, for both sets of fans."
United have won 19 league titles but Ferguson recognises that making it 20 this season would have to be regarded as one of the most enjoyable for the fans because it is City they are competing against.
"I think our fans would look upon it as special one because it's against their most bitter rivals," said the United boss.
"I don't think you can get away from that. If you asked any of the fans, then I know what they'd say. For me, it's another league."
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