Working in partnership matters even when you write on your own! How and why?
For me, this means seeing writing as two distinct processes. One is the fun creative side of getting everything down on paper or on screen. The second is the editing process where you tighten your story up and really give it muscle by getting rid of anything and everything that does not contribute to moving your tale onwards and upwards to its conclusion. I love editing. I love the sense of the story improving as I spot repetitions etc I didn't see in the giddy delight of creating new characters etc. I love the sense of getting rid of what isn't helping the story.
So where does the collaboration come in? By accepting these are two distinct processes and not trying to do both at the same time.
Give your creative side free rein and enjoy the ride. Don't let your inner editor spoil that. It's not time for them to come in yet. Once that side is finished, then recognise the fact that all stories are improved (and therefore stand a better chance of publication) by good editing.
See editing as what gives your stories the wings to fly! I do and find this side of things fun as a result. Nothing is going to beat the heady thrill of creating something new but it helps enormously to know nobody has ever produced a truly terrific story in one go! Everyone needs at least a second draft! Good luck.