People often say things like, "I don't want to do X if you don't," and don't really mean it. They mean they want to, but they are willing to do what the other person wants. This is not ideal; it's not coming to agree. So how should it work?
Jack: Jill, I don't want sex if you don't.
Jill: Are you not attracted to me?
Jack: That's not it. You are attractive. But look, there are thousands of attractive girls out there who I don't want to have sex with. I think it's a bad idea. Most of them are total strangers. In each case I could be persuaded otherwise, if we met, got along, discussed it, and so on. But right now, I don't want sex with all those people. Nor with you. You could persuade me otherwise, by explaining why I'm wrong not to want it, and then I would change to want it, but presently I don't.
Jill: Why don't you?
Jack: I know it's important to you not to.
Why important? Well, one possible reason is: Jill is considering becoming a Nun, and they won't take her if she's not a virgin, and she wants to keep that option open at the moment.
Another possible reason is that Jill is confused about abortions, and scared of birth control failing (she had a scare with a late period last year), and feels she can't have sex again until she works that stuff out, but is really stuck on those issues and doesn't know when they will get better.
Another is that Jill is currently in a monogamous relationship with someone else, and doesn't want to cheat.
So anyway, how do we know that Jack is serious that he doesn't want to while Jill doesn't? How do we know he isn't just saying it? Here is a test:
Jill: Oh baby! Let's fuck!
Jack: Umm, Jill, you're drunk.
Jill: Nah, I'm fine. But I changed my mind. Let's have sex now.
Jack: No. You're drunk. I don't want to right now. If you really changed your mind, we can do it later, when I feel better about it.
Jill: Screw you. Aren't you attracted to me?
Jack: Yeah, but I'm not comfortable with this. Why did you change your mind, anyway?
Jill: I just did. And I'm in the mood now. I may not be in the mood again for a long time if we don't do it now. C'mon.
Jack: Please don't try to threaten me to have sex. I don't want to without understanding why it wasn't a good idea yesterday but is today.
And so on. Jack passes the test by avoiding sex even though Jill is willing, because he cares about her in general, and not just about what she will agree to do tonight. But this is a commonly known situation, that many people would get right. Let's try a harsher test:
Jill goes on a vacation for a month, to relax and stuff. Jack wants to stay home and pursue some hobby Jill doesn't share. They are both happy with this. Jill returns, and that night they go out to a romantic dinner, and have a moonlit walk on the beach. Or pick whatever romantic stereotypes you prefer. Or even imagine they do their own thing that they like, but you wouldn't. The point is it's nice.
Jill: *whispers* Jack, I think I'm ready to have sex.
Jack: Really? Why?
Jill: I thought through some things, and I think it's a good idea now. *kisses Jack* (They've already kissed before lots, say.)
Jack: *breaks kiss after a few moments* Jill, I'm happy about this, but I need to understand why.
Jill: It's fine. Let's not ruin the mood. *runs hand along Jack's chest*
Jack: But my best understanding is that this is a bad idea. I need to be told why to change that and want to.
Jill: That's sweet of you, I'm glad you're thinking of me, but this is what I want, and you shouldn't say no to me to protect me. It's my decision, alright? *smiles seductively*
Jack: But *I* am not comfortable with this. Why aren't you telling me what changed so that it's a good idea now?
Jill: Alright, sorry, I will.
This was a much better test. I believe many people would pass the first test, but fail the second. They don't want to feel guilty about taking advantage of a drunk person. But in the second scene, Jill has thought out what she wants, and as she points out, Jack shouldn't decline just to protect her. Here, he has to actually not like the idea himself, because he's internalized some of Jill's old reasons, and now he himself cares about them, and he needs to see the solution to them to feel good about sex, exactly like Jill must see the solution to them to want sex.
If Jack hadn't acted the way he did in the dialog, and had agreed to sex, we would know when he originally said he didn't want to if Jill didn't, he wasn't doing it right. If Jack will have sex when Jill says she wants to, then it shows he didn't value the same things Jill did, that made her not want sex, he only valued not hurting her, fighting with her, etc. Which means he didn't really agree with her the whole time, and it was a problem. It might be expressed as Jack saying, "I do want to have sex with you, but even more than that I don't want to hurt you." This is much better than nothing, but if Jill cares about what Jack wants, then she will feel pressured.
Hi guys, 2015 Elliot here to add a few comments:
The big thing here is, if you genuinely change your mind, the new opinion is now part of you, alone, by yourself. Real mind changing means you're now a true believer who'd advance the cause for your own reasons. The reasons that used to be someone else's arguments to you, are now part of you, and you'd carry on even if they fell over dead. (For personal issues it might become irrelevant if they died, but the concept applies to persuasion about anything.)
A good test of whether you believe something yourself is whether you'll still argue for it when the person who was persuading you changes their mind. Were you just trying to be on the same side as them and will be happy to drop it now? Or will you be curious what more they learned and unable to change your mind further without new information?
People understand this better with impersonal topics. If you persuade me of socialism, you'd expect me to still be a socialist when you leave the room, and to argue for it with others. If I'm not going to advocate socialism on my own, I'm not really persuaded that it's true and important. But with personal topics, people often mix up deferring on an issue with actual persuasion.