One of the things that bites even experienced writers from time to time is giving insufficient consideration to the ways their characters react to things. (Me blogging about this has nothing to do with the fact that I just turned in the copyedit for The Far West and ended up deleting or rephrasing about twenty different character reactions because I’d gone with people rolling their eyes every time. Nope. Nothing to do with that at all.)
There are actually three parts to this, and each of them is equally important: there’s the way the character sees what’s happening, followed by his/her emotional reaction, followed by the character’s physical expression of his/her emotional reaction.
Let me unpack that a little.
In any given situation, whether it’s emotionally stressful, embarrassing, a fistfight, a laser battle, or just a couple of people shooting the breeze after work at the coffee shop, each character will have a different internal, emotional reaction to it that depends on that particular, individual character’s personality and life experience. Even something as simple as the boss saying “No, don’t do that right now” may feel like a stinging reprimand to one character, an oblique warning to another character, and a friendly reminder to a third character, depending on each person’s level of confidence/insecurity, his/her past history with that particular boss, his/her past history with authority figures, etc. Each character will have an emotional reaction to their perception of whatever is going on, which will also vary, and each character will express those emotional reactions in a different way, depending on their personality, confidence, background, culture, etc.
For most characters, the only part of this that actually gets put into words on the page is the physical reaction part. Except in omniscient viewpoint, the reader only gets the narrator/viewpoint-character’s thoughts and internal reactions to any given event; everybody else is limited to what the point-of-view character can see them do (i.e., the physical expression of the reaction). It is therefore all too easy to race past the “what the character thinks just happened” and “how the character feels about what just happened” parts and go straight to shrugging, smirking, eye-rolling, and hair-tossing, without really considering whether this character would actually do any of those things in this particular situation, or thinking about what they might do instead.
For example: start with a situation in which someone has just dropped a metaphorical bombshell in a room full of people: This is the One Ring, Darth Vader is his father, that boy pulled the sword out of the stone, whatever. If the writer is in a hurry, and most of the characters aren’t very plot-important, you get things like “A stunned silence fell” or “Everyone turned to look.” And sometimes, that’s exactly what you want, because you want to keep the focus on the main character or the ring or the sword or whatever, and not on all the different reactions.
If, however, there are six major characters present, the writer needs to give a bit more thought to the matter. Since the situation is a Big Revelation, there’s probably not going to be a lot of different perceptions about what is happening (though the guy on the end who’s been established as paranoid and a bit too sensitive to personal slights may be less concerned about the revelation and more worried about why nobody chose to inform him about this before telling lesser folk). And yes, everyone is going to be astonished – but people will be astonished in different ways.
The girl next in line from the paranoid is rather sweet and sheltered; she’s going to be astonished and full of wonder. The woman next to her hates surprises; she’ll be astonished and she’ll resent being made to feel astonished. Next in line is her husband, who’s been telling people forever that something like this was going to happen; he’s going to be just as astonished as everyone else (because he didn’t really expect this to happen now), but he’s also going to gloat. The eight-year-old who’s been bored out of his mind by most of the meeting doesn’t know enough to be truly astonished; he’ll be surprised because everyone else is, but his main emotion is likely to be “Finally! Something interesting!” The jealous sidekick is going to be astonished and jealous; the reluctant hero is going to be astonished with a large leavening of “Oh, gods, why me?” and so on.
Once the writer has sorted out all the various ways people feel about what is happening, she/he has to decide how each person shows those feelings in character. The paranoid guy may glare (if he’s really upset about not having been told first)…or he may smile and nod and try to give the impression that he knew all along. It depends on what he’s like. The rather sweet girl may look on in wide-eyed astonishment, or blush and look away; the woman who hates surprises may stiffen or look angry, or her face may go blank; her husband may grin or look smug or triumphant or straighten up as if he’s the one who just pulled the rabbit out of the hat. And so on. It depends on what each person is like.
And of course, for writers, this cuts both ways: early in the book, the writer may well be finding out what each character is like by assigning them different reactions and body language and then figuring out why each of them did that, while late in the book, the writer will probably know the characters well enough to tell what they’d feel and figure out how they’d express it. Readers, though, only have the actions (and perhaps some thoughts from the POV character), and have to figure out what the characters are thinking and feeling from the way they behave. Hence the importance of making each character’s reaction – both emotional and physical – characteristic and unique to them.