I used to get this quite a lot, and still do sometimes.

What helps me is reminding myself to just start coding _something_ small and very very simple, however imperfect. If I didn't I would concoct hugely scalable and secure architectures and systems in my head. I would go on and on like this for hours and possibly days. It would only really stop when I came up with another idea for a project.

Twitter/Facebook/Netflix etc etc weren't built from scratch like we see them today; they evolved from imperfect, probably insecure, probably slow, probably unmaintainable code.

Just try to write something and take it from there.

I think lots a "techy" people experience this so don't beat yourself up and I'd be interested to hear what others do.