Arsène Wenger feels conceding so soon after being reduced to 10 men was the key factor in his side's home defeat to Chelsea.
Diego Costa scored the game's only goal midway through the first half, just six minutes after Per Mertesacker was sent off for a professional foul on the Spain striker.
Despite losing, Wenger was encouraged by the spirit his team showed and says they should take "even more belief" from the setback.
think we had a good attitude and fantastic spirit despite the negative result today, I think we should come out [of this] with even more belief
"It was disappointing as we couldn't really play with our real team for 90 minutes," the boss told Arsenal Player. "I was very disappointed because in recent games we have lost we have had really harsh decisions against us [like] at Southampton and today.
"We had such high expectations today. To lose the game the way we did is really frustrating today and difficult to accept.
"The difficulty was that we went straight away down at 1-0 and we had to attack without being at 0-0 which means you expose yourself at 10 men, but what can you do?
"I think we had a good attitude and fantastic spirit despite the negative result today, I think we should come out [of this] with even more belief."Copyright 2016 The Arsenal Football Club plc. Permission to use quotations from this article is granted subject to appropriate credit being given to www.arsenal.com as the source