The Barclays Premier League champions slipped seven points off the pace being set by derby rivals Manchester United when they succumbed to old boy Adam Johnson's lone strike at the Stadium of Light.
City head for Norwich on Saturday under orders from manager Roberto Mancini to become more ruthless in front of goal. Hart told citytv: "It's how football goes sometimes. I don't think we have not tried or not given 100 per cent or not shown quality, it's just that it wasn't there and we need to turn that around quickly."
United's lead may be commanding at the halfway point of the season, but both Mancini and Sir Alex Ferguson know from experience that is far from decisive. Indeed, having chased down their neighbours during the final seconds of the last campaign, City will be confident of doing the same again with plenty of football still to be played.
Hart said: "It's difficult every game to win. To be leading is difficult and to be chasing is even harder, so we will see. Hopefully it will do what it did last year."
Norwich had gone 10 league games without defeat before losing 2-1 at West Brom on December 22, and they were unable to make amends on Boxing Day when Chelsea left Carrow Road with the three points courtesy of Juan Mata's first-half strike.
The Canaries could be forgiven for approaching the fixture with some trepidation after losing the corresponding match last season 6-1 on a day when Carlos Tevez plundered a hat-trick and Sergio Aguero struck twice.
Adam Johnson completed the scoring on April 14 and by coincidence, he found the back of the next on Wednesday, although this time wearing the red and white of Sunderland against City.
Hart was unable to keep out his former team-mate's long-range 53rd-minute strike on a day when opposite number Simon Mignolet frustrated the visitors with a string of fine saves.
Hart said: "We dominated the game and lost, but we have got to move forward. Their goalkeeper had a special game, which he has done against us recently. He is a good keeper. We just couldn't quite get it in."
Source: PA
Source: PA