I do this too, but it's more like I feel un-inspired by it?
Usually I'll let it sit for a week, re-read it and then scrapping it if I still don't like it.
It's pretty common I believe, to scrap ideas like that.
Tbh, I let an idea sit for nearly a year before I go into scriptmaking, but it's just so I'm sure that I'll complete it.
However, I go straight to thumbnailing after feeling done with the idea, instead of scripting, as it's easier for me to see the whole thing. (Writing/scripting first is actually really good!)
I've made comics, that I didn't finish because I hadn't the whole plot planned out, but thought I could do it anyway and figure it out as I went. (It didn't end up well, I scrapped it completely after doing 20+ pages and hated every ounce of it xD)
Few tricks that has helped me:
1.) Don't write the first thing that comes to your mind. Whether it's a great idea or not.
Great ideas comes twice.
Believe me, they do.
2.) Plan the whole thing. Or at least get the general basics down, details can always wait.
3.) Are you still passionate about the idea as you were 3-4 month ago? Write it down! Chances are it'll be a sticky one
4.) Push yourself through it. It will feel boring and bland, but motivation to keep trucking is what helps most of the times.
5.) Only YOU can tell your stories.