Part of winning is believing you can win. Each person has different thresholds for that belief, and based on comments like that it's obvious that Jenson's threshold is lower than Lewis'.
Or look at it another way, managing your expectations is easier for some people, I tend to be realistic about my expectations and tend to be pleasantly surprised when I do better that expected!
Maybe it explains the different in driving styles, maybe it explains why you support one driver and I support another. One is a pessimist one is an optimist? One is a fighter one is a survivor?
In any case, the point is Button believes it's all over for him. Maybe he's taking into consideration his abilities and weighing them against what he feels he can do and in this case it's little.
I'm saying that Lewis probably doesn't feel the same. So perhaps Button is saying he's willing to help Lewis in his WDC bid?

McLaren clearly has the best car on the grid. That still counts for something right?