Trust is an important element of BD/SM, it takes time to build trust in a partner and fully understand each other. I've been with my current partner for 22 years and she reads me like a book. Sexually oriented, erotic pain has been a good part of our relationship and she had to gentle me along for a bit when we first met and now I know she will never injure me intentionally.
There's a big difference between erotic pain play and actually injuring someone.
Mistress ! No ! Please ! Don't ! Stop !