What's the formula?

I was asked by my brother what I do to get ready to write a new book.  Do I plot everything down on paper?  Do I ponder and analyze anything before I start?  Surprisingly no.  I guess if I had anything on the left side of my brain doing something like that would make sense.  But since I don't, I don't.  All I need is a story in my head.  Nothing huge, just an idea really and then I picture the main characters in my mind.  And then . . . I sit down and write.  But you'll hear the words formula a lot.  If you go to any writers conference you will hear the words formula over and over.  Boy meets girl, tons and tons of problems to keep girl away from boy, then everything is wonderful and perfect and then, oh no, wait, something even more horrible comes up that threatens the happiness and joy of everybody and then thank heavens by the last chapter everything is perfect and the guy gets the girl and you have your happily ever after. If you're sci-fi, add in a few space crafts and creatures.  If you're suspense, add in a murder. Etc. Etc. But that, boys and girls is the formula.  Are there other formulas out there that work well?  Of course, but this is the main event. Think of most of your classics and they'll fit. Take Pride and Prejudice, my fave. Love it! People have loved this book forever and it's still relevant.  It's still read and it's still enjoyed.  It's amazing what you can do with a good formula, isn't it? The question is, what are you going to do with it?