To the orriginal point:
I think "Keeping them safe" is acurate if vauge. The Dom(me) *imho* who takes on a new sub, or who is advising a new Dom(me) needs to teach them how to go about things in a safe way. Things like safe words, sanatizing toys, rope work and blood flow/restriction, setting up safe meetings. And to not scare them away from the lifestyle! Everything else is gravy.
As to a mind set..
Everyone is different. I think if you wanted to you could start sorting subs into sub-groups and find commonalities in those groups but there is no one set caracteristic that you'll find in EVERY sub. I also think we're all effected by our first introductions to the lifestyle.