I'll add a simple understanding from a males perspective.
In time and in many sessions of play, there will be more and more instances when the Dominant will come to be in parallel with the submissive. In those instances and may at times be rare, the Dominant feels the incredible and overwhelming love to protect the submissive. That is in some views "the reality check" of how far to go. Despite the urging of the submissive, that moment will have a line draw in the sand until visited and discussed the next time the dance continues.