Hooks or introductions to a new fantasy?

Some refer to the first line of a story as the hook. I like to think of it as the introduction to a new fantasy.  I don’t know how many times I’ve had an idea pop into my head that wouldn’t go away. Today, you can see many of them in the opening lines of my books. Or I have filed them on my list “New Ideas” for a project in the future. I’m not saying that they are still the exact phrases, in fact they very seldom are.
I remember for My Cheeky Angel that it all started one morning when I woke up and thought about how happy I was with my life. I laid there for some time seeped in my good fortune and the thought came to me—what if a heroine woke up feeling the opposite. What if she hated her life, herself and her future?
My original line had undergone a huge metamorphosis because it had been more like…  Annie Hynes hated everything about her life. I changed it repeatedly until I found a positive way to write what she was feeling without saying those ugly words. This is how the sentence reads in the book…
Today is the first day of the rest of your life.
Many times, when I take my notes to enter the lines on my list, I realise that they aren’t as catchy as I had originally thought. Sometimes it’s just a matter of revision but oftimes, I’ve lost the enthusiasm the words first inspired. Guess that happens to all of us. I suppose it depends on our mood, or the circumstances of where we’re at in our work. But when I can’t get rid of the image the words evoked, almost always there’s a book that will follow.
The other day, as we were travelling along the highway, I was reading a wonderful story written by one of my favorite authors and she had mentioned a puppy. Instantly the following line came to me and I had to grab my purse for the notebook that’s always there and jot it down.
The ball of white fur had sharp teeth. And at this precise moment they were embedded in the material of his jeans.
Immediately, I could see the action happening and an inner smile followed. I knew I wanted to write a story with this opening. At the moment, I have three books plotted and rolling around in my head, needing to be written. But this could be a short story…...??  More about hooks in my next blog. But in the meantime, I'd love to know if this kind of thing happens to you? Even if you're not an author, do these kinds of ideas pop into your head and make you want to write about them?