Dear Auntie Deborah, How do I stick with my story idea and finish writing it? 
Some writers can take an idea and launch it into a story while writing, but most of us can’t — or else end up revising many times to whip that shapeless manuscript into something that resembles a true story. Your description of losing motivation suggests that you, like me, need to have more structure in place before beginning.
What do I mean by structure? I need to have a hook or inciting incident — the action, situation, crisis, or decision that fuels the first part of the story. Then something goes wrong (or right, or unexpected) and spins the story in a new direction — that’s the first plot point. I need to know what it’s all building toward, and also the feeling or flavor I want to leave the reader with (sadness, triumph, satisfaction, chocolates on the pillow?). I need at least 2 or 3 characters I’m in love with, although I don’t necessarily need to know what happens to them. I write all this down, do flow charts and maybe a map or two. If I’m submitting on proposal, I’ll need to flesh it out into a proper synopsis plus the first 3 chapters, but for writing for myself on spec, that’s enough to get me going.
If these concepts are unfamiliar with you, I encourage you to learn more about storycraft and the journey from idea to plot/character/dramatic arc. Ideas aren’t a bad place to start, they’re just not enough.
Deborah: It is as important to know which advice to ignore as which to pay attention to! Without knowing the sources of your opinions, I can’t evaluate their validity, but — BUT — I am always leery of anyone who tells me how to fix problems in my own work. This was true when I began writing on a professional level 35 years ago, and it certainly is true now. What helps me are comments like, “I’m confused about x,” or “This didn’t work for me,” or “I don’t care what happens to this character.” In other words, careful readers marking where they had problems. Then it’s up to me, the author, to discern where I went wrong and how I want to remedy it. (This is how my publishing editor and I work together, by the way.)
My second point is that learning to write and working on a specific project are two different things. A project problem may highlight a skill you need to strengthen, but someone telling you how to improve it makes it their story, not yours, and isn’t likely to help you improve as a writer.
I wonder if you might fare better by not showing your work to anyone until it is completed to the best of your ability. Otherwise you run the risk of distorting your artistic vision to please others so much that you lose your authentic creative voice. When you are ready for feedback, seek out trusted readers (who need not be writers themselves but who have keen sensitivity to their own reactions) or writers a little ahead of you in their careers. Make it clear what kind of feedback you want: What worked for you? What didn’t? Where did you lose interest? Was the result satisfying? And leave the nuts and bolts of prose craft for a separate discussion.
Deborah: By speech, I am assuming you mean dialog. Dialog is a wonderful storytelling tool, but like any other tool, there are some things it’s great for and some things it’s not. If you find yourself with page after page of “talking heads” — nothing but dialog — you might be trying to use it for purposes it isn’t suited for.
So what might dialog be used for, and what other storytelling tools might you substitute? Does it advance the plot? (Alternative: narrative description of action.) Does it reveal character? (You bet, but so do interior monologs/thoughts and description of action/reaction.) Does it heighten tension? (It can, especially between characters, but so can description and pacing. Think of what happens if a character pauses before replying, or looks away, or shifts posture or vocal tone — all these things require narrative, not dialog).
One way to think of this difference is to imagine your pages of dialog as a movie script. That’s all it is, just what each character says. But a movie is much more; it’s acting, scenery, music, and so forth. That’s where your narrative and description come in. If the movie were just talking, we’d all go to sleep. So imagine what you see and hear (not words, but other sounds) that isn’t dialog, and weave that in between the speech.
In other words, if you can accomplish the same storytelling goal without using dialog, don’t use it. Try that as an exercise, and see if it highlights those areas where dialog shines.
This happens to us all. I’ve been writing professionally for over 35 years and it still happens to me! The most important thing to remember is that it will pass. The second most important thing is that if you can manage to be curious and nonjudgmental, and to observe your thoughts, you can learn interesting things about how your mind works.
In order to get my internal critic out of the way, I change media. So instead of composing at the computer keyboard, I switch to longhand, or dictating/voice-recognition software, or an old-fashioned typewriter. I act out scenes aloud. I switch creative fields altogether. I dance or play a musical instrument or sing or go bird-watching or knit or paint…all of these are ways of expressing yourself, just using different parts of your mind and body. Then I can return to the story at hand feeling more confident and refreshed.
I repeat, be gentle with yourself. Think of this as a common bond with every successful writer. If the words aren’t flowing, sidestep them. They’ll be there when you’re ready to return.