The Inciting Incident is one of the most critical plot points in your story: it justifies why your story is even happening, so it needs to be well-thought out and executed for maximum impact.
The Inciting Incident is the transition point between your Introduction, where your main character is introduced and their day-to-day established, and the Rising Action, where your MC is going to grow, learn about the big bad, wreck havoc, make mistakes, and inch closer to that Climax of tension, suspense, and resolution.
The Inciting Incident needs to have a large enough impact that your MC is either willing to leave their normal day to day, or it needs to pose a great enough impediment to prevent them from coming back or returning to that day 0 state.
To prevent shocking your reader, try to include foreshadowing for the Inciting Incident somewhere in your intro, maybe through dialogue, in something they hear, or even in an interaction, thought, or behavior. Think of how you can keep this foreshadowed thread active throughout the book to avoid the Inciting Incident becoming a "Convenient Catastrophe".
Convenient Catastrophe's are inciting incidents (or other events) that happen for a singular purpose and then are forgotten about. The issue with this is that significant events always have a lasting impact on the world or the main character, so without any resolution, Convenient Catastrophes often feel shoehorned in and disconnected from the story.
Inciting Incidents and other significant events are going to be memorable to your MC, so as you unfold the Rising Action, have your MC think about it, experience emotions, or change behaviors as a direct result of the Inciting Incident. Doing this will make your inciting incident believable and realistic to the reader and add depth to your narrative and MC. You may even want to include a deeper resolution for the Inciting Incident in your Climax or Conclusion, by maybe having your MC come to accept what happened, repair the damage done, or establish a new normal in spite of it or because of it.
I hope you've found this helpful!
This video explores this topic as well, I hope you enjoy!
Happy Writing!
~MJ