The perception has been put forth by (was it) Nani or that French defender (both from Man U) that Arsenal are nothing but a 'training school' for footballers. This, including the other taunts and lack of trophies instills a lack of killer instinct.
Added the fact that we have to recall Lehmann, and score plenty of own goals, is a recipe for disaster.
If you also notice, when we draw or lose, we concede first, only to score late after 70min's or so.
We can score at the 45 - 55min mark. Then concede at the 70-85min mark.
Now, that is a team who does not have the killer instinct.
Look at Man U. Do they rotate their keepers? Do they ever, ever recall their old keepers?
Look at how Rooney celebrates his goals. Look at how Van Persie & Arasharvin celebrates. Do the Arsenal faces look like they can eat you up? NOPE.
Rooney's face is such that of a raging bull.
Our's lack the confidence. The Ommph. The face that Keown, Wright, Vieira had when they scored, or fell behind.