Mentally we've never been tough enough, as we don't get exposed to the same intensity as they do.
Our instincts in situations of pressure and intensity end up costing us, and their instincts in the same situations end up benefiting them.
They play in a more intense competition, and the best players get to play in the Origin games too, which is up an even higher level, and possibly the highest level of all.
Through these experiences they learn how to handle the pressure. They're not super human. They make mistakes, unforced errors etc etc. The difference is they'll be put back in that same pressure situation many many times during a season, if they don't adapt and learn then they're gone and someone else will take their place. To survive and excel their instincts evolve to make the right decision under pressure, and to stay composed when the heat is on.
Our instincts aren't able to evolve in the same way because the competition over here is not as intense, big teams can get away with mistakes and errors all day long, and so our better players don't need to learn or adapt to survive in the competition. Some players get to experience a few truly intensive encounters a year, but most do not. If our players had it week in week out, with the same intense Origin series too, we'd beat them on a regular basis.
Even though they have the edge on us, there is absolutely no reason why they can't be beat. Yeah they know how to handle the big game, but they don't always execute, far from it. They're only human, and they do make errors, more than people think. Everytime we go at them with real heart and controlled aggression, taking the fight to them, they really don't like it, and they start to wobble, we've done it many times to them, we just haven't been able to stick with it and capitalise.
To beat them when it matters we've got to go to a level we've never been to before and not just for 80 mins, for the next 4 weeks!
The best thing for British rugby would be to beat them in the final, to be 4 points up in the last 10 mins, and to not crack, to not let go, to be stronger, to be the very opposite of what they expect us to be, composed, and focused under extreme pressure and fatigue, to be better than them. Mentally stronger.