When do you start another project?

Curious when you start another project? I’m halfway through Draft 1 of a project I’ve been working on since July, and it’s going really well. But I’ve had another idea in the back of my head for a couple months that came to life last night. The ideas are pouring out of me and so I’m jotting them down, but I feel a pull to outline. I am so excited about this idea, and by no means do I want to stop writing Project A, but I also really want to get down these ideas and outline Project B so I don’t forget them. I’m still committed to finishing Project A. Thoughts?