I definitely write from either a line of dialogue or a conversation, then work backwards to find the emotions. Often, I'll write the story just as huge chunks of dialogue and then I'll go back to fill in the scene details, the emotional motivations, etc. I didn't realize, until Merry posted it, that I do that exact same thing where I stop right near the end of the story and sort of...retrofit the emotions, make sure they're all what I want them to be, then write the end.

I find that if I write from the emotions, I end up being horribly "telling not showing" I'm not a very evocative writer, so my emotional scenes tend to be something like, "And John was really happy. Yay."