The following is a paragraph from Stephen King’s On Writing that I feel sums up how interactions should go:

The situation comes first. The characters–always flat and unfeatured, to begin with–come next. Once these things are fixed in my mind, I begin to narrate. I often have an idea of what the outcome may be, but I have never demanded of a set of characters that they do things my way. On the contrary, I want them to do things their way. In some instances, the outcome is what I visualized. In most, however, it’s something I never expected. For a suspense novelist, this is a great thing. I am, after all, not just the novel’s creator but its first reader. And if I’m not able to guess with any accuracy how the damned thing is going to turn out, even with my inside knowledge of coming events, I can be pretty sure of keeping the reader in a state of page-turning anxiety. And why worry about the ending anyway? Why be such a control freak? Sooner or later every story comes out somewhere.