(Or ... When "when" works better than "as," and participles part ways with reality.)
One of the most common logical errors I see when editing is actions happening at the same time when it's impossible for those actions to be anything but sequential.
These two ducks can simultaneously stick their heads in the water, but they can't do it while also eyeing a person with bread on the shore (since their eyes are underwater, silly).
Obvious, right? So how on earth does this problem occur so frequently? Well ... certain constructions imply simultaneous action, even if that isn't the writers' intent.
Those pesky participles
The first culprit is participles ---- those troublemaking modifiers prone to dangling or getting misplaced. Present participles (verb form ending in -ing, like "looking," and "singing") are the primary reason for the common (and simplistic) advice to avoid -ing words. Past participles usually end in -ed, but don't let that fool you, they're prone to the same problems as present participles. And even if your participles aren't dangling, they can still get you into trouble by creating impossible situations that undermine the credibility of your writing.
Eyeing my bag of moldy bread, the ducks ducked* under the water and stuck their tail feathers in the air. X
"Eyeing" is a present participle, and "eyeing my bag of moldy bread" is a participial phrase modifying the noun "ducks." Even though it's modifying a noun, a participial phrase usually describes something that's happening during the action that noun is performing. So this sentence is saying that the ducks were eyeing the bag of bread while simultaneously ducking under the water and sticking their butts in the air. Which is impossible.
The example sentence could also start with "while" and mean the exact same thing, since the "while" is implied with present participles. Mentally inserting the word can help you determine if a participial phrase is causing a logic issue in your own writing:
While eyeing my bag of moldy bread, the ducks ducked under the water and stuck their tail feathers in the air. X
When a participial phrase comes first in a sentence, it's especially easy to think you've written consecutive actions. Since eyeing the bread is the first action mentioned, it seems to make sense that the action was performed first. Notice how it's easier to spot the impossibility when the participial phrase is moved to the end of the sentence:
The ducks ducked under the water and stuck their tail feathers in the air, eyeing my bag of moldy bread. X
What to do instead
When you're writing a first draft, please don't worry about these kinds of things. The last thing you need when you're trying to be creative is an imaginary editor looking over your shoulder. Get your ideas down. There's plenty of time in the revision and self-editing stages to hunt down misbehaving participles.
And when that time comes, there are numerous ways to revise. Which one works best depends on the rhythm of the surrounding text.
After eyeing my bag of moldy bread, the ducks ducked under the water and stuck their tail feathers in the air. ✓
The ducks eyed my bag of moldy bread, ducked under the water, and stuck their tail feathers in the air. ✓
The ducks eyed my bag of moldy bread, then ducked under the water and stuck their tail feathers in the air. ✓
The ducks ducked under the water and stuck their tail feathers in the air after eyeing my bag of moldy bread. ✓
Having eyeballed my bag of moldy bread, the ducks ducked under the water and stuck their tail feathers in the air. ✓
The exceptions
(Because there's almost always exceptions.)
Participial phrases can be used to show sequential action if the first action is quick and the second action immediately follows.
Opening her eyes, she was stunned by the vista before her.
Getting up, he grabbed the folder off the bedside table.
If I overthink it (which copyeditors are prone to do), these can still bug me a bit. After all, you can't see much of anything until your eyes are completely open. But using participles this way is useful for showing swift actions that flow into each other, since making the actions clearly consecutive would slow down the pace.
She opened her eyes and was stunned by the vista before her. (slower)
Once she'd opened her eyes, she was stunned by the vista before her. (even slower)
And participial phrases are useful for showing a series of rapid actions that may or may not be simultaneous.
He raced down the trail, dodging tree roots, stumbling over the log that marked the edge of the forest, scrambling to his feet, not stopping to catch his breath until he was in the open sunshine of the meadow.
Obviously this isn't the best sentence ever written, but it does have a breathless quality that contributes to the tension and rapid pace of the scene. And an overzealous editor who tries to make sure every. single. action is clearly sequential runs the risk of laboring the writing and slowing the pace—and working against what the writer is trying to achieve.
He raced down the trail, dodging tree roots. He stumbled over the log that marked the edge of the forest, then scrambled to his feet. He didn't stop to catch his breath until he was in the open sunshine of the meadow.
Not terrible, but it definitely slows down the pace.
Not all -ing words are participles
There are plenty of words that end in -ing: nouns like "string," prepositions like "during," verbs like "bring" and "sing." It's pretty obvious that these are not what people are talking about when they advise writers to avoid -ing words, but gerunds can still cause confusion.
Present participles and gerunds look exactly the same, but do different things. And sometimes people get so leery of participles (which are modifiers) that they also become nervous about gerunds (which act as nouns). But gerunds don't cause the same problems as participles.
Eyeing my bag of moldy bread was rather rude. Don't those ducks know not to look a gift horse in the mouth?
Here, "eyeing" is a gerund, and "eyeing my bag of moldy bread" is a noun phrase that is the subject of the sentence and the verb "was." The words may be the same as above, but the function is different. Notice that no comma follows "eyeing my bag of moldy bread," because a comma should never separate a subject and verb—unless there's a pair of them surrounding a parenthetical phrase, as below.
Eyeing my bag of moldy bread, which was all I had to offer, was rather rude.
Since the comma following the noun phrase can mislead the reader into thinking it's a participial phrase and cause them to stumble part way through the sentence, recasting can be helpful with sentences like the one above.
Eyeing my bag of moldy bread was rather rude, especially since it was all I had to offer.
As, While, and When
Another common cause of illogical simultaneous action is the word "as." I don't see this discussed as frequently as participles, but I come across it often when editing.
"As" and "while" both mean during the time that (at least in this context—both words have other meanings as well) and indicate that two actions are occurring simultaneously. While "while" doesn't seem to trip up writers, for some reason "as" does.
But "when" is more flexible. Like "while" and "as" it can mean during the time that, but it can also mean at the time that or just after the moment that. (I used it above—"when editing"—in the first sense. I could have also written "while editing" or "as I'm editing.")
So "while" and "as" are used for simultaneous continuous actions ...
My son was working on his homework while I cooked dinner in the kitchen.
or to describe continuous actions that are then interrupted by singular actions ...
As Sam was jogging down the street, a pigeon pooped on his head.
but only "when" can be used for single actions that interrupt a continuous action.
Sam was jogging down the street when a pigeon pooped on his head.
So if you find yourself writing something like ...
Sam was jogging down the street as a pigeon pooped on his head. X
or
As he arrived, the police were waiting for him. X
... you need to consider what kind of actions you're describing, and whether "when" would work better than "as." Even though arrivals aren't usually instantaneous (unless, you know, magic), once you've arrived, you've arrived, so "when" is the correct choice:
When he arrived, the police were waiting for him. ✓
Another common problem with "as" that I see is a character speaking a short phrase as they are doing are doing multiple consecutive actions. For example:
"I'm almost ready," he said as he put the lunch in the picnic basket and carried it to the door. X
Speaking a short phrase can happen simultaneously with one action, but it can't occur simultaneously with two consecutive actions. He either spoke the phrase while putting the lunch in the basket or while carrying it to the door, but not both. Sometimes the simplest fix is removing the dialogue tag.
"I'm almost ready." He put the lunch in the picnic basket and carried it to the door.
Though now it sounds like all the action happened after the dialogue. If it's important to retain the sense that he spoke in the middle of the action of putting the lunch in the basket, you can do something like this:
"I'm almost ready." He finished putting the lunch in the picnic basket and carried it to the door.
And notice how making dialogue a told continuous action rather than a shown singular action works seamlessly with the two consecutive actions.
He told me the story of what happened last night as he put the lunch in the picnic basket and carried it to the door.
You may be wondering if readers will actually notice nitpicky little things like this. Truthfully, many won't, but that doesn't mean they won't notice something feels off, that the writing lacks the professional polish of the books they're used to reading. Precise language helps you communicate your ideas clearly to your reader. So these little fixes that line editors do can make a big difference to the overall feel of your writing—and rather than changing your voice, they actually help it shine through.
*Repetition deliberate. Am I the only one who finds the word "duck" hilarious, and double "ducks" even funnier? I had a grand old time playing with repeated words/sounds in this post, but I wouldn't advise this kind of repetition in fiction narrative, since it draws attention to writing mechanics (and thus the writer) which is the enemy of reader immersion😘.