How do I motivate myself to write?

I’ve had several book ideas over the past 4-5 years. I’ve written chapters for one, developed my characters and outlined essentially the whole thing.

Then I just… don’t write it.

I think the fear of it being terrible stops me from even trying, which I know is incredibly dumb.

I should just write, see where that takes me. But I just come up with these ideas and outlines and don’t even share my writing anywhere they just sit in my notes for ages. How does one get over that fear and just doooo it?