No Writing Is Wasted Writing

Writing is hard. Getting that first nugget of an idea on to paper is exciting then quickly exhausting. If you're a writer, the process becomes obsessive. You think about scenes whilst cooking tea, you stop mid-walk with the triumph of a fresh solution to a writing dilemma. You basically start living your story. And then that glorious day arrives when you have that story down, the whole thing, and you think, with a sigh of self-congratulations and relief, that you've done it.
Ah. But then you re-read it, or you ask some encouraging friend or relative to read it, and then comes the blast of truth: what you've written is a mess. My first draft was overloaded with adjectives and adverbs. What do you mean I shouldn't use words ending in -ly? It was also full of plot lulls and holes. And the whole thing was written in third person when first would be much better.
So, I began systematically rewriting. I took out a few darlings (though not many) and worked and reworked scenes, changing characters as I went, adding in new ones. As with my paintings, I'm not terribly precious about my writing. I can be quite cavalier. I horrify my family with how easily I can tear apart a seemingly finished painting because it's not quite right. I take the same approach with my writing, tearing out parts that haven't worked and not worrying too much, trusting my instinct.
Rewrites done. And again, that wonderful sense that I've finished.
Ah. But, another read through, some more trusted opinion and no, of course it isn't finished. More rewrites. So having spent countless hours rewriting the first draft, you're doing it again, cutting out the sections you'd not long ago added in, taking out a character you'd though would add a fresh dimension but hasn't. So what was the point of those first lot of rewrites when all you're doing now is rewriting again? Were all of those hours a waste of valuable writing time? Short answer, no.
When we rewrite, we are polishing, honing the story, clarifying scenes, perfecting dialogue, editing out plot holes. When we rewrite the rewrite, we're doing the same thing but this time (and this is important to remember when you're pressing delete on swathes of polished, unworkable writing) you're GROWING your writing. 
Imagine the first draft as the shoot from the seed of an idea. Second draft, leaves unfurl, third draft, some hard pruning but the shoot grows thicker, stronger, taller. Fourth, fifth, hundredth draft (the number of drafts all depends on how you work - it's not a reflection on how 'good' you are as a writer) your story is a confident, resilient tree.
You simply can't grow a tree from a seed in one draft - however much we'd like to hope we can. Rewrites are the rings inside the trunk of the tree. They become invisible to the reader of your final draft, but they're in there, in your writing, making it strong.
Lots of successful writers tell new writers to be fearless. I think that's especially true when rewriting. Never keep something just because you've spent hours writing and polishing it if it's not working or is no longer relevant to the story. Never mind that you're deleting hours of painstaking work. You've not wasted your time. You've spent those hours creating, nurturing, growing, the final draft. The final, euphoric, ah.​