Reading some sound advice in another blog about getting the details right caused me to think about those things in your writing that can rip your reader right out of the reality you're trying to create for them.
I remember, as a kid and inelegant teen, how I would often bring my author parent a sample of my latest creation. I was eager for praise and generally disappointed in my expectations. My parents were never like that, regardless of the occasion. I had to earn my praise. Every time I turned in a short story or a poem it was subject to a scathing critique which always began with comments about the grammar and structure.
"But the idea… do you like the idea?"
After a while I stopped bringing my little mangled mouse offerings of juvenile writing to leave on the parental doorstep. My ego had been wounded too many times. For a number of years I didn't even write - why bother?
Now I'm here to tell you that all those little comments that drive you crazy when you ask for critiques are necessary. Bad grammar and structure will thwart your readers. Typos will exasperate them. Getting details wrong will wrench them from your world. If a sentence doesn't agree with itself or you forget to tell the reader who is talking you will lose their focus. Do your research. Nothing irritates readers and fans so much as a faulty detail.
You think I kid? I would have LOVED the movie 3:10 to Yuma only the movie makers insulted my intelligence and the intelligence of everyone that had ever gone to Bisbee, Arizona. In the movie they went for the old spaghetti western trope of the windswept and isolated dusty town in the middle of a flat bleak nowhere whereas Bisbee is built in a wooded gulch with crazy steep streets and houses clinging to the mountainside. All they had to do is name the town something else and I would have been happy. Because they called it Bisbee I was annoyed and then angry. It broke the spell. The movie became a mere movie.
A lot of things can destroy the illusion you are seeking to create when you write so pay attention to the little things, to make sure your sentence makes sense, to those stupid typos that creep in everywhere (he grabbed her by the waste is disgusting and will break the mood), to the details that reveal you know what you are talking about or you simply don't. When you are the author, you are the authority, so don't lose it in the details.