It is known in group psychology that the most intransigent conflicts are between two people who share most but not all personality qualities; or alternative, because person X reminds person Y of their own worst impulses.
On a related note, I once more have to apologise to the nation for another interminable thread where Sir A. Davinescù and I rhetorically give each other kicks in the shins. I have just realised the extent to which is probably looks like a twin brother and sister fighting.