With only three wins in seven games in all competitions, Sir Alex Ferguson's side are having to endure a period of inconsistency.
United had to settle for a draw against Birmingham at the weekend after being knocked out of the FA Cup by League One Leeds.
Fletcher: Still hopes to be celebrating with United at the end of the season
However Fletcher - who will miss the Barclays Premier League match against Burnley on Saturday through suspension - says some of the criticism has been over the top.
'Everyone wants to shoot you down when you are successful and you need to have the character to take that on board and fight back.
'That is the challenge. You learn from it and it is what being part of this club is all about. You get used to and respond to it.
Giving United the Blues: Cameron Jerome scores for Birmingham as United were forced to settle for a draw last weekend
Fletcher, who has become one of United's most important players over the past couple of seasons, added on the club's website: 'When you are young and naive it can affect you. But I had very experienced players around me when I first broke through who pointed out the reality of it.
'The older ones have passed it down. The likes of Ryan Giggs, Paul Scholes and Gary Neville told me not to worry about it because they'd experienced it and you get through it.'
United, one point behind leaders Chelsea having played a game more,have escaped the big freeze with some warm weather training in Qatar.
Will he be pointing the way towards yet more success? Sir Alex Ferguson has enjoyed his time in Qatar this week
They are due to arrive back today to complete their preparations and Ferguson hailed the trip as a success.
'It's been a memorable experience and the complex we used is without question the best I have ever seen,' said the United boss.
'Not only that, the operation is so well managed that it has made our stay very easy and relaxed. We hope that this journey is not our last here.'
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