X: You say you are happy with me. That's what you think you are saying. And you conclude that I am the sole necessary condition for that happiness. But what you don't know is that you are actually saying you are happy with me in this particular so-and-so situation, and it is by ignoring this background variable that your reasoning becomes erroneous. I am not the sole necessary condition for your happiness. Put you and me in a different situation, and the outcome may be entirely different. But then, it isn't reasoning that you are doing, is it? You are expressing an emotion, and emotions have no regard for logic.