Don’t look back until you’ve written an entire draft, just begin each day from the last sentence you wrote the preceding day. This prevents those cringing feelings, and means that you have a substantial body of work before you get down to the real work which is all in … the edit.
No writing is wasted. Did you know that sourdough from San Francisco is leavened partly by a bacteria called lactobacillus sanfrancisensis? It is native to the soil there, and does not do well elsewhere. But any kitchen can become an ecosystem. If you bake a lot, your kitchen will become a happy home to wild yeasts, and all your bread will taste better. Even a failed loaf is not wasted. Likewise, cheese makers wash the dairy floor with whey. Tomato gardeners compost with rotten tomatoes. No writing is wasted: the words you can’t put in your book can wash the floor, live in the soil, lurk around in the air. They will make the next words better.
Editors can be stupid at times. They just ignore that author’s intention. I always try to read unabridged editions, so much is lost with cut versions of classic literature, even movies don’t make sense when they are edited too much. I love the longueurs of a book even if they seem pointless because you can get a peek into the author’s mind, a glimpse of their creative soul. I mean, how would people like it if editors came along and said to an artist, ‘Whoops, you left just a tad too much space around that lily pad there, lets crop that a bit, shall we?’. Monet would be ripping his hair out.