Help!

I've been writing since I was eight.. whether it be idiotic short stories about whatever anime I was crushing on at the time or just some shit. I've been running into the same problem now that I've gotten older. I CANNOT finish a story. I will come up with an idea, flesh out my characters, move around a bit within the story if I become too focused on one part and even venture out to places where I can get inspiration if I am suffering from writer's block but either my insecurities get the better of me and I abandon the story altogether or another idea comes to mind that sounds better at the time and even still the cycle would continue.

My question to the writers here is:

- How do you continue a story and actually finish?
- How do you not let the constant worry that it will never be good enough and that you suck psych you out ?
- How do you continue on?

Could anyone give me some type of advice? I have a story that I would like to write and finish but I'm terrified that the same fears that plagued me and also halted me to stop all of the other stories will strike again and I really want to finish this. Can anyone help?