I recently one of my critique partners was having trouble with a story and I ended up giving her this piece of writing wisdom:
"The problem with fiction is it needs to be truer than life or people with think 'that's convenient!'"
The suspension of disbelief is an important aspect of any work of fiction. It is required by nearly every story told, seen, or read, except maybe those that like to break the fourth wall.
or are purposefully nonsens-icle, like rabbits with pancakes on their heads
This means, unlike life, we can't have coincidences or apparent coincidences show up on the page or we risk the reader seeing behind the curtain and realizing we are not wizards of words, but charlatans selling them deus ex machina snake oil with a side order of lazy writing. And if we do this, then we can't blame our readers if they decide to take out the pitchforks and roast our books with flaming hot reviews.
So, what can we do to encourage our readers to suspend their disbelief? First, everything on the page needs to be truer than life. There needs to be a cause and effect. There needs to be foreshadowing. If there is a reveal in the story or a twist, then the reader needs to have enough clues leading up to it that they have a chance to figure it out on their own.
If you have one character another character, you can't just do it for fun or slap stick humor. There needs to be some reason for the act that the reader can see and understand. Nothing should come out of left field unless you've shown the reader left field and given them some kind of hint that they should pay attention to left field. Oh, look! There is the guy our main character kicked earlier... with a steamroller!!!
You might notice the kick doesn't have as much impact as the steamroller... this isn't just because the steamroller is bigger and squishier, but also because we have a context. One character was kicked by another and this sets up the motive for revenge... with a steamroller!!! Overkill, yes, but at least there is a setup that explains the action. There is reason to suspend our disbelief and accept that there is a possibility of someone running another person over with a steamroller.
We could set this scene up even better by mentioning the steamroller earlier in the story, having the character who gets kicked be the driver of the steamroller, or any number of other pieces of foreshadowing. The key is to make sure the reader can sense something coming. Even if they don't anticipate exactly what it is completely.
So, just remember, setup is an important aspect of helping your readers suspend their disbelief. So, don't forget it! Whether it's a steamroller or a shark. We need to see it coming... unlike this ninja...