Need help with finishing my stories?

So my problem isn't that i don't have inspiration...it's that i have too much inspiration. i begin writing a story, and then something happens and i get an idea and start working on THAT story, and then i get a different idea and...you get the point. This has been going on since i started writing- i have found unfinished comics from when i was eight. Right now i'm currently working on the plots of 11 books (not including the ones i temporarily abandoned) and 9 comics. there is an advantage, i mean i get to change things i wrote years ago, for the better, but obviously the major disadvantage is that i can't seem to finish a project. In total i have only completed one novella. What can i do to help me stay dedicated to one story? Any suggestions/advice? Thank you, any help is appreciated.