If trust is so important between partners why would you need a safe word?
One of the first things I learned about BDSM, when I really started exploring it, was the use of the safe word.
I used to play with a Dom who I will call “John”, for the sake of privacy and all that good stuff. John was one of the first Doms that I played with, and a very considerate partner. I trusted him, knowing him outside of BDSM circles, but because I was still new to kink play, he wanted to be sure that I was comfortable with anything that we did, that he did not hurt me, and that I did not feel bad about anything that we did. We discussed what each of us wanted to explore and he had me choose a safe word, something that I would not use in our play normally, so that if I said it, he would instantly know to stop. My use of the safe word, and I did use it a few times with John, was not a signifier that I did not trust him. It was a signal to be used any time I felt, for whatever reason, that I needed to use it.
I had a very good introduction to the safe word, but I found it took a very long time to truly understand what it is. The safe word is not just a replacement for “no” or “stop” or “too much”. It does not replace trust in a BDSM dynamic; that you use it at all shows that you do very much trust your partner.
To really answer another question, I need to answer another and dispel a couple of myths.