At some point in the first chapter the main character will have to deal with something. Some issue will arise, a problem will present itself, a revelation will be made, a decision will be considered. This inciting incident will set the story into motion, and tell the reader the sort of thing they can expect. The tone, the theme, the level of realism. Sometimes it occurs on the first page, maybe even in the first line. Or it can take a while for it to emerge, allowing us to get to know the characters and the setting.
The inciting incident doesn't necessarily have to be a problem the main character will be dealing with throughout the whole story. It can be one of a series of events that lead into whatever the story is about. But it has to capture the reader’s interest as it is the first point of entry into the story proper.
Big or small, of domestic or global importance, two things need to be considered. Firstly how are you going to present whatever it is? And secondly what are the consequences?
If for example the problem is that a woman discovers her husband has been unfaithful, the manner in which she discovers this counts for a lot. It would be very simple for her to find lipstick on a collar or a voicemail on his phone, which would very clearly indicate the infidelity, but it would also be very obvious and predictable.
Even though the problem you're presenting may be fairly familiar (after all there are only so many things people are concerned about) the way you reveal it to the reader needs to be as interesting and engaging as possible. If it is too straightforward and simplistic the meaning will certainly be clear but only in the way the meaning of a cliché is clear.
The more inventive and unexpected you can make it the better. You would also do well to show the moment as it happens. Having a character recall how it happened or having people talk about it, is not as powerful as seeing it.
Once you have the moment down, it's important that the reader is aware of what is at stake. If the woman, having discovered the man is cheating, divorces him and then gets on with her life there is nothing really very interesting about that. The problem, whatever it is, should be only the start and not easily sorted out. You need to have consequences that develop from that inciting incident and lead characters into their next move.
It can't just be a matter of personal preference or action based on a whim. They have to do something because doing nothing is not an option. If the woman decides she needs to sort things out and goes on holiday by herself, leading to further adventures and a journey of self discovery, it will be a more powerful story if the reason for going on holiday is more than, “I’ve had enough, I’m off to the Bahamas.”
If you can make it so it isn’t just a random thought, but comes out of character, and I mean in a specific way, then it will read in as much more engaging. If her therapist tells her to not seek revenge but to take time for herself to think things over, and she sells her husband’s beloved Porsche and uses the money to pay for her trip abroad, you can see her actions both give us an idea of how she feels and the kind of person she is.
How you get into the inciting incident is just as important.
Let's say the inciting incident is that a woman, Doris, is concerned about her daughter’s online activities and breaks into her e-mail account to find out who she's been talking to. She discovers many e-mails from a woman claiming to be the girls real mother and insisting that Doris kidnapped her when she was a baby.
So, we start with a very normal maternal concern for a daughter behaving oddly that leads into a plausible reason to invade the kid’s privacy. Information revealed is unexpected and has an emotional impact on our main character. Her next move could be one of many things but it is clear that she has to do something. The mother wouldn't just close the computer and wait for the next thing to happen.
What you shouldn't do is have the mother to say to someone, "You’ll never guess what I stumbled across today. I was just cleaning Debbie’s room and...”
You need to show it happening and you need to show why. Often, because the writer knows where this is leading and that the discovery of the other woman claiming to be the mother is going to interest the reader, the build up is rushed through and left vague, just a way to get from A to B. But the reader is not in the same position as the writer. The build up is as important as the reveal and needs to be not just believable but interesting in its own right.
This particular scenario is just one I plucked out of thin air. The scale of the problem can vary greatly, but it should resonate with the themes and overall narrative. In the above example I imagine there would be issues of trust, family conflict, secrets forced into the open or even some element of the effect of the Internet on our lives. It could turn out to be about the relationship between mother and teenage daughter, or it could be about a woman who used to be a CIA spy; it doesn't really matter.
The inciting incident is not about whether this will prove to be a plot-driven or character-driven story because both types require problems for the main characters to deal with.
What is important is that the problem is presented as something the character can't ignore. And like with any moment that affects the main character it should be interesting, memorable and unpredictable.