The Rules, maybe
This goes under the assumption that Jacob and MIB grew up as brothers, or at minimum, childhood friends.
I think the Rules are based in something from childhood. For example, when you play Hide-and-Seek, one rule is that you can’t peek once your eyes are closed until you finish counting. Similarly, Jacob and MIB probably played games that had several rules, such as: 1)Â you can’t get me if I’m touching the banyan tree, or 2) no messing with outside girls because they have cooties. The Rules probably got extended to more adult-like behavior as they got older.
I thought of this as people have brought up the Rules, such as Jacob/MIB or Ben/Widmore. One says that you broke the rules, that you can’t break the rules, which is always followed up with some sort of slight or scoff.