WBTSOYP = writing by the seat of your pants. It means sitting down and just writing, no plotting involved. I'm not advocating WBTSOYP over plotting or vice-versa in this post. Everyone has their own process and every writer has to use the process that works best for him or her.
I started out a "pantser," but it didn't work that well for me. I'd get a scene in my head and work out from there. The problem was that I would get stuck sometimes, bogged down in places where I'd written myself into a corner. Or my characters started out half-baked and I would have to go back and revise significantly. The pantser books I started out with -- Raven's Quest was one -- turned out fine...after lots of revising and rewriting.
Eventually I worked myself into a pattern of plotting because of this, but leaving space to move a little. That's how I do it now. I write the synopsis before I start the book, flesh out the middle (the hardest part of the book to keep momentum for me) and *definitely* figure out the end.
Pantsers say that they can't write the book after they've written the synopsis because they feel like they're done, the story has already been told and there's no excitement left in it, no discovery. But I don't feel that way. Writing the novel after I write the synopsis means I get to watch the story unfold. It's kind of like the synopsis is the trailer and the novel is the movie. I might pretty much know the story after I've seen the trailer, but I still want to see the movie.
Usually my story ideas start with a character. There's some type of personality I want to write, or I want to write about a person in a certain situation. I figure out how I want him or her to grow and change throughout the story and the plot develops from there. For example, with Water Crystal it started with Angelo. I wanted to write about a man who worked for the bad guy and was loyal to his employer until he became disillusioned. Bianca has her own journey and also grows and develops from page one to the end, but it was mostly Angelo's story.
Anyway, I'm just thinking and babbling about this (with really no specific point in mind) because I fleshed out the synopsis for my next EC book yesterday and then plunged right in and wrote 4k. Today I'm here at the day job, but I'm dying to be at home writing. I'm really wanting to tell this story. Good thing I'm only here three days a week. By Thursday I'll be full-speed. (Only half speed until then.)