It is true that every writer stands alone, even those that collaborate as they have to go off to write "their bits" before coming back and swapping notes with the other one(s) in the project. We have to judge whether our work is strong enough to submit and, if there is a choice of places to submit to, which is the best one. We have to judge whether we have edited a piece enough or if it still needs work. The call is with us and we are going to get it wrong. The joy, of course, is when we get it right and a piece is published.
This is where meeting other writers, whether at conferences, online, at courses etc., is invaluable. There is nobody like another writer to know exactly how it feels when you're struggling to get the words out or who knows the joy of the words pouring out and work going well. You do have to share this sometimes for the sake of your own sanity!
I learned a long time ago no writer is a competitor to me. I write as I write. I cannot write as you would. We all bring our unique perspectives to what we write - and that is the great thing about it!