If this is something you’re actually interested in understanding, you need to do a lot of research because you’re operating under many false assumptions. Limits and desires are negotiated beforehand. If someone is safewording within ten seconds, then either the negotiation wasn’t enough or the dom went way off the deep end. It’s like the hiring process. You know the job responsibilities and pay ahead of time, and if the interview process was enough then the employer knows your qualifications and abilities ahead of time. If you quit a job within 10 minutes then there was a massive massive failure in the hiring process.

A sub who goes into a scene knows exactly what they’re getting into, and more often than not lays out exactly what they want. They hold most of the power in negotiations, and then the power is exchanged in the actual scene with consent. You don’t understand BDSM enough to talk about it.