There's this problem a lot of writers have when it comes to the first chapter. How much do you explain, how much do you leave out, and how do you know?

What you see often in critiques and edits is a request for more information. And writers get huffy and say it's fine the way it is. You don't need 1000 pages of backstory.

And that's true. And editors and reviewers tend to struggle to say:

There's a fine line between making the reader ask questions and leaving the reader confused. The reader doesn't need to know who stole the ham sandwich or why or what the relationship is between the sandwich thief and the person who made it.

But if you're opening with the theft of the sandwich, they should be able to know the basics (a ham sandwich has been nabbed). I've read people's mysterious openings where I knew a ham sandwich was being stolen because the blurb told me so, but when I sit down to read it, I don't know what the heck is going on. You could interview me right after and I'd come up with: someone did something.

So how do we handle mystery?

There's no need to be vague about everything. If you are, you'll quickly blur the line between what's important and what's not. You might even lose the focus of the scene. You'll just make readers think harder about stuff they shouldn't have to and that can get old real quick, especially if someone is deciding whether or not you're worth a shot.

"The ham sandwich sat on a rectangular object, about six foot long with four wooden legs."

It's a table. Put the sandwich on the table. If you aren't planning on doing anything special about this table now or in the future and it isn't your quirky alien protag narrating, just let it be a table and let the reader focus on the real mystery.

Now see how much you wrote that isn't vague or mysterious. Is it balanced?

Let them feel like they're holding onto a couple straws (even if they're lies). Readers need to walk away with the idea that they know what's going on. Most readers will happily tell you that they don't need to know everything right away, but they also don't want to feel like it's the night before a chemistry exam and they haven't gone to class all semester.

In a mysterious location a mysterious cloaked figure is waiting in a tree/bushes while mysterious people talking about something mysterious appear in range. Our mysterious figure is going to do or steal something when a mysterious hand catches her from behind.

This is not memorable. This will not further your cause now or down the road. I don't have anything to talk about. But throw a pet chicken in to foil the sandwich thief's plan and all of a sudden I'm paying more attention (and slightly distracted so I don't feel like asking as many who, what, where, why, how's).

Okay so your reader comments saying: is that a ham sandwich? and you think, YES. I DID MY JOB. I MADE THE READER ASK A QUESTION. Now they're hooked.

Wrong.

Your reader should be asking the question or moving in the direction you want them to. Asking a question doesn't mean they're thinking about your story. Asking the question you wanted them to doesn't mean you're doing it right. It can mean they just don't know or don't understand why they can't know it yet (see #6).

Readers sometimes ask interesting and unexpected questions and that's okay and you just have to deal with it. Every time I go on tours I seem to be that one jerk who manages to ask a weird question the tour guide is totally clueless about.

But if you're using a mysterious element in your opening, you should already know what that element is, and what you want the reader to be thinking about it. If they're questioning things that aren't supposed to be mysterious, you may have a problem. If they're questioning things that are supposed to be mysterious, see below.

One of the things that bothers readers is when a story has something mysterious for no damn reason. I see this a lot with NAMING CHARACTERS.

For some reason people decide that our protag can be the mysterious figure until the very last sentence of chapter one (or the opening of chapter two) where the narrator suddenly decides to use their name. Or they refer to the man in the room as just a man, and then when it's dramatic enough the protag adds, "Dad" to the end of their sentence.

Sometimes this work. A lot of the time (and not just for names), readers smell the dramatic ploy like a bit of burning plastic in a new car.

You don't have to be loud. You don't have to be obvious. But your reader only has the story to refer to. It can be as simple as our first person narrator (and sandwich thief) not encountering a person until chapter two. If you look back, the evidence is there. They're stealing a sandwich and the only witness is an angry chicken. It's reasonable. If you wanted to include the protag noticing her name on grandma's fridge or reminiscing about her mother scolding her about taking what don't belong to her...Well there you go. But you're still mostly covered because you've got a valid reason.

For the sake of your story, go and have a look and see if you can find what went wrong (if anything did). Sometimes you'll have that person like my bad critic who highlighted things like "she grabbed a chicken leg" and responded a few sentences later with "I'm confused. Where did you say she grabbed a chicken leg?"

Other times you get a reader who paid careful attention but you dropped the ball. That's why you need to check before you go off saying, "You're supposed to ask that so I'm in the right."

How much do you explain (enough not to impede the story), how much do you leave out (enough to give your reader a sense of understanding/direction), and how do you know (you carefully examine what your reader is saying!)?