Say I'm 20,000 words into a WIP. I love my characters and every little thing in my life reminds me of them. It's kind of weird, really. I'll be at a coffee shop and talk about a minor character that works in my own fictional coffee shop. One that's not real. My friends give me blank stares. Or someone will mention piano and I'll instantly think of my main character. I'll be sitting in the park and thinking about how much my fictional friend would love it. So my characters are a part of me, to say the least. It's almost a little creepy.
But then I'll get SIS. A new character will pop in my head. Or, mostly, a new plot. And I have to write it. Generally, I can write some notes down and go back to my WIP. But some times, these new characters are egotistical brats and MAKE me write about them.
That's when SIS is bad. Because I feel like I'm cheating on my old characters/plot. I just recently started a new book; not only because I had a horrible case of SIS but because my old WIP (the 20k one) needs a full rewrite before I continue. And I needed a break.
But a "break" has turned into a long time. I feel like I abandoned kids, but at the same time this new idea is pulling me and I don't want to give up on it. I plan on eventually finishing both, but now it's going to take me a lot longer than I expected to finish my initial WIP.
When a new idea is tugging at you, what do you do? Listen to it, or remain consistent?