A common feature in relationships is the giving of ultimatums: “Do this thing or I’ll break up with you,” and the like. This appears to be a bargaining tactic, the offering of two things and the choice between them. In reality, both parties tend to know that it isn’t really a choice, it’s a demand combined with a threat. They’re saying, “Do this thing [that I want and we’ve been arguing about] or I’ll punish you.”
This sometimes works. Some people just roll over rather than deal with the confrontation. Some realize that the threat is an idle one, and ignore the ultimatum entirely. Sometimes the ultimatum-giver is forced to make good on the threat, which they don’t actually want to do. Rarely does everyone come out of such a situation happy.
Most advice columnists will tell you to never make ultimatums, because of this. I present an alternate rule:
Never give an ultimatum unless you would be happy with both outcomes.
Which means that you can make ultimatums for relationship-ending offenses. If you know that if your girlfriend doesn’t stop smoking you’re going to break up with her, but you’d be happy staying with her if she did, then go ahead and put the choice in her hands. Just make sure you’re prepared to break up with her if she picks the cigarettes, and that you’re okay with that.