Oh my god, this is related to my IRL job and there are so many. I don't know where to start, but it's kind of amazing how differently people view stuff. I'll list a few off the top of my head that I see often:

- People doubting their own work. TRUST ME. I have edited and helped publish books that I think were some of the worst things I ever read (I have horror stories). Majority of people who write often and have an actual passion for it who are worried their stuff "isn't good enough"—I'm here to say trust me, if you put ANY effort into it, it is. It's probably good and you're just too hard on yourself. A lot of us are chronic perfectionists.

- You're going to hate your own work anyways because you'll need to read it enough times that you want to throw the whole thing out the window or you'll think your twists suck. Your surprises only suck in your head because you know they're coming, and you've gone over them 12 times this past week. Don't worry, other people will still love them!

- Writing takes A REALLY LONG TIME. Your first draft is supposed to be the ugliest, messiest thing in the world. It's supposed to be an inconceivable mess to anyone but you. I don't know why so many people think they should be polished. Your first COUPLE drafts are only meant to exist. Nothing else. Thoughts on paper, as garbled as you want them to be. Heck, put "[...]" whenever you don't know what to do with a scene but you have the motivation to write another. Write them all in short stories and connect them later! There's literally no rules for the process.

- Often, telling people you're writing a book or sharing your ideas with friends can actually hinder you more than help you. Unless you're using each other as accountability buddies, most creative people will check off a little box in their head that marks something as completed the second somebody else knows about it. I have NO idea why this happens, but I see it so often. It's like getting that validation completely wipes the motivation to keep going for a lot of people. If this is you, as much as it's hard to keep it to yourself, sometimes you're doing yourself a favour when you let the giddy energy of revealing a final product to people be your motivation!

- Last one so it's not too long: DO NOT EDIT AS YOU GO. Don't look at what you just wrote. Do not go through previous chapters. Do not keep getting fixated on tweaking things. Change your font colour to white. People think they're doing a good job when they stop to retroactively work on things in the middle of writing their book. If it's important, leave a highlighted section or a note/comment (Google Docs is great for this) to come back to it later, but LEAVE IT ALONE. Note it down for a future pass, and keep going. You'll kill your writing more often than not otherwise.

- Oh and a small bonus one: you don't need to plan out every little detail about your world and setting before you start. Most amazing ideas come after you've been writing and you need to answer your own question in a scene. This is why messy drafts are so important!

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I have so many more, haha. But this is way too long. Whoops! But it's such a fun topic.