Arsenal manager Arsene Wenger says last season's home defeat by Swansea "killed" his side's title hopes and led to a "virus" of negativity among fans.
The 2-1 loss in March, which followed a 3-2 defeat at Manchester United, left Arsenal six points adrift of eventual champions Leicester.
Wenger was heavily criticised by fans after his side lost to the Swans, who return to Emirates Stadium on Saturday.
"I must say that the negativity comes very quickly," said the Frenchman, 66.
"It is a virus that travels very quickly and goes away very slowly."
The Londoners finished last season in second, 10 points behind Leicester.
Thierry Henry, Arsenal's record goalscorer, said he had never seen the club's fans as angry as during the defeat by Swansea.
This time, the Gunners face the Welsh side on the back of five successive wins in all competitions. They are third in the Premier League, two points behind leaders Manchester City.
"I believe at the moment the vibes are positive," Wenger said.
"We have reduced distance with the top teams. We have to continue to get to the next level.
"Fans are part of our game and they have the right to be happy, not to be happy. My job is to focus on my job and trying to make them happy."