Readers have noticed.
These things happen, and you shouldn’t beat yourself up too much, but if you self-published (which more and more people are doing these days), fix it as soon as you can.
If you are published by a traditional publisher, ask them to fix it. It’ll take longer, but the sooner the process gets started, the better. … of course if a book doesn’t have a second run, you may be stuck with that typo. (Another reason I like self-publishing and print-on-demand.)
Mistakes happen. Writers, and even editors, are human. But letting an error sit there, if you’re trying to be successful and sell your book, makes no sense. If the typo is in your marketing blurb on Amazon or elsewhere, it’s even more vital you fix it now. A typo in a one-paragraph block of copy is a bad sign. I can’t speak for other book buyers, but 99.9% of the time I will not buy a book with a typo in the promo copy. My exception is when buying from a friend—but I will let the friend gently know about it.)
I’ve heard it expressed that writers who make a lot of spelling errors do so because they “see through” the words to the concepts behind them—they might not spell well, but they are better at describing and reporting things.
When I worked at a daily newspaper years ago, I knew a reporter whose copy was typically full of spelling errors. He would arrogantly declare, “It’s the copyeditor’s job to fix typos!” It was annoying, but he was an excellent reporter and storyteller, and his attitude was tolerated because he got the job done. The copyeditor just read his work more carefully. At this very same newspaper, there was a guy we called “Prima Donna” because he was consistently late on deadline while trying to write the perfect lead and make sure every sentence flowed. His reporting was less than stellar, and, as I recall, his writing wasn’t all that hot either, despite his nit-picking.
I think there is a balance in between these two extremes. I don’t think having typos makes you a deeper thinker or a better storyteller, and I don’t think being anal about getting everything right makes you a dry, boring writer. I can’t imagine any writer who doesn’t have typos in the first several drafts. If a writer obsesses about typos at that stage I would think that would block the flow of inspiration.
Obviously if you think typos are no big deal, you can ignore this. But to me, it’s another advantage to self-publishing. You can fix your errors rather easily. Let the critics see your story and your words. Don’t let them be distracted by mistakes.