I think if you are going to have fulfilling and safe feeling sexual experiences, you really do have to be willing to turn someone down if they reveal themselves to be a bad fit in any stage of the sexual negotiation process, and be able to bring the sex to a halt the moment that you're not enjoying it and don't want to be doing it anymore. This really is a vital skill to develop in order to ensure that you are actually enforcing your own boundaries, and it will lead to you having sex that is more in line with your actual desires too.
The first time that I stood up in the middle of riding a guy and went "nah this sucks I'm going home," and left right then and there was the day that i unlocked unlimited power. we tell people a lot that a sexual partner can say no to them at any time but we don't teach people how to actually honor their own no and bring things to a stop for any reason and that leads to a lot of people feeling like they have no choice but to be dishonest, and having begrudging unfun sex.