Communication means being willing to speak difficult truths.
It means putting honesty and transparency above comfort.
Communication means speaking your total truth, but also being prepared to hear the truth of your partner(s).
In a D/s, PE, or TPE relationship where control is at a premium, a couple cannot survive unless transparent communication is at the heart of the relationship.
If we look openly and honestly at all relationships, it's clear that communication is the single factor that can make or break even the most solid of romantic foundations.
It's not just the BDSM/Kink community that needs to keep communication at the fore: it's every couple, every poly arrangement, every single human being that wants to get what they need and provide their loved one(s) the same service.
If you do not ask, you cannot know.
If you do wish to know, you must ask.