My dad used to tell us. A brother never fights with someone else against his brother. You ALWAYS stick up for your brother. I think my dad was John Wayne. I think it was his way of extending his protection to the playground through his covert operatives. Namely my older brother, who was known to think that only he could hit his brothers, everyone else couldn't touch us.
I think the feeling of knowing that at any point in a problem you would have guaranteed help. That's what my dad set up in us. And now I have carried that over to a few very close people. It's not always fighting either, just being there in a time of need. To KNOW that you have a partner, a friend, someone who is fully invested in your problem, it is now theirs. I am thankful I have a God better than all 5 of my brothers.
brothers do fight, but they don't hate.