i think it's mainly to do with amount of handling, especially handling when they're young. My brother has a brb that i wouldn't hesitate to hand to our grandmother, presuming she was inclined to hold it. That snake is totally docile and to my knowledge has only ever nipped my brother a few times when it was very young and still nervous.
Tbh, i can't really imagine having a brb and not handling it on a regular basis; they're so pretty, and since they hide so much, you never see them unless you pull them out. I guess that means that if i ever have one, it'll probably end up being pretty calm.
yea i have a baby brb & it strikes sometimes when i try & take him out the tank, once he's in my hands its the nicest snake ever. He strikes every single time after feeding. So this week i fed in the cage