Why Did Some Brit Tribes Surrender So Quickly?

Rome spent centuries cultivating a reputation for being ruthless to her enemies and kind to those who surrendered. The flip side of it, however, is that romea had every reason to be exceedingly harsh on the tribes who refused to surrender. So the screws really were being turned on the britons at this point in history. But i don't think the average farming briton would have noticed much of a difference between british and Roman rule.