Reading aloud is the cheapest edit

I once sent a client a proposal with the sentence "we'll the homepage first." I had read that sentence maybe nine times. My eyes glided right over the hole where the word "build" should have been, because my brain knew what I meant and quietly filled it in. The client noticed in about four seconds. I only caught it myself later, reading the proposal aloud to my wife to brag about how clean it was.
That gap between what I wrote and what I thought I wrote is the whole problem with proofreading your own work. You can't proofread something you wrote five minutes ago, because you're not reading it. You're remembering it. Your eye skims the page and your memory supplies the rest, and the two of them are very good at agreeing with each other.
Reading the words out loud breaks that agreement. Your mouth has to deal with what's actually on the page, one word at a time, in order. It can't skip ahead and it can't fill in a missing "build." That's the trick, and it costs nothing.
Why your ear catches what your eye misses
When you read silently, you're pattern-matching. Skilled readers recognize the shape of words and the shape of sentences and move on, without processing every letter. That's what makes you a fast reader. It's also what makes you a terrible proofreader of your own stuff, because the pattern your eye matches against is the one already sitting in your head.
You're not reading it. You're remembering it.
Saying the words removes the shortcut. You hear the actual rhythm of the sentence, and a surprising amount of bad writing is really just bad rhythm. A sentence that runs on too long leaves you out of breath before the end. A sentence missing a word makes you stumble. Two sentences in a row that start the same way sound like a stuck record the moment you hear them, even though they looked fine on screen.
Here's a thing to try right now. Open the last email you sent that mattered, the one to a client or a prospect, and read it aloud at a normal speaking pace, in your actual voice, with actual breath. I'd bet money you trip on at least one sentence. Every writer does, because the screen was never going to tell you.
What it catches that spellcheck won't
Spellcheck and grammar tools are fine for what they do. They find the word that's spelled wrong. They don't find the word that's spelled right and means something you didn't intend, and they don't find the word that simply isn't there. "Form" instead of "from." "Manger" instead of "manager." A whole missing verb. Those sail straight through every tool I've ever used, and they land in front of the person you most wanted to impress.
Reading aloud catches a different category of problem too: the kind that is technically correct and still clumsy. Phrasing that doubles back on itself. A clause buried so deep the reader needs a map, which is usually the same paragraph where you leaned on "actually" three times. None of that is an error a tool flags, but all of it makes your writing harder to trust, and you hear every bit of it the second you say it out loud.
This matters most on the writing that carries weight: the homepage that's the first thing a customer reads, or the proposal that's asking someone to spend real money. These are exactly the pieces where a stumble costs you, and exactly the pieces we rush because we want them out the door.
There is a newer reason this matters more than it used to. When you write with an AI in the loop, the draft comes back smooth and easy to skim, which is exactly the condition under which your eye stops reading and starts remembering. Reading it aloud is still the cheapest way to catch the sentence that sounds right and is quietly wrong. It is a habit I teach when I help teams learn to work with these tools without getting burned by them.
The only thing stopping you
You already know how to read and you already know how to talk, so there is nothing here to learn. The reason most people skip it is that it feels a little silly to sit at your desk reading your own emails out loud, especially in an open office. Mumble if you have to. Read it to the dog. Step into the hallway. The mild awkwardness lasts about thirty seconds and the payoff is that you stop sending sentences with holes in them.
I read everything aloud now before it leaves my hands: proposals, posts, the descriptions I write for my own plugins. It is the first trick I hand every writing client, and it is the fastest way I know to hear whether a piece deserves a second draft. It adds two or three minutes to a piece of writing and it has saved me from more small embarrassments than any tool I've paid for.
The next thing you write that someone's actually going to read, read it out loud before you hit send, top to bottom, in your real voice. You'll hear the problem before they do, which is the only place you ever want to hear it.