Way back when, the English poet and philosopher, Samuel Taylor Coleridge, formulated the concept of "willing suspension of disbelief."
Coleridge coined the term as a means to justify the use of fantastic or non-realistic elements in literature. Since that time, the notion of "willing suspension of disbelief" has been applied to many things, most often in the realms of entertainment as well as con-artistry.
According to Coleridge's theory, suspension of disbelief is quid pro quo: Readers, viewers, audiences, and marks agree to suspend their judgment, i.e., what they'll accept in terms of believability, in exchange for the promise of something, either in the form of entertainment or personal gain, or something else.
Some Nigerians, the ones who send us emails notifying us we've either won a lottery we did not participate in or that we've been left millions of dollars by some African royalty, are attempting suspension of disbelief. Hollywood regularly attempts suspension of disbelief in big ways, whether it's a jarhead becoming an avatar in the form of an alien being on a distant world or Bruce Willis's "Die Hard" character engaging in all kinds of death-defying stunts that, in real life, would kill him quite quickly and easily.
Never, in the history of suspending disbelief, has it been more notably and routinely attempted than on the internet. Virtual anonymity is the Holy Grail of would-be belief-suspenders. When or where else have so many attempted such bullshit in so many ways? Whether it's in the form of them telling others who and what they are or in photos posted on forums and elsewhere.
The term "suspension of disbelief," as it applies to photography, takes many forms: From trick photography to manipulated alterations meant to dazzle, confuse, or simply make a subject look like something other than it was. (When snapped.)
In pretty girl shooting, we routinely use lighting, exposure, post-production, and more to engage viewers and, hopefully, convince them to suspend their sense of disbelief.
The real trick when suspending disbelief is in the SoD-artist's ability to suspend it without going over the top. In other words, most viewers will only suspend their sense of disbelief to a point. As a rule, the more or less informed a viewer might be about certain photo techniques, the more or less they are willing to suspend disbelief. Sometimes, of course, the attempt to suspend disbelief is quite obvious yet viewers are still willing to "believe" the image because it's cool, fulfills fantasies, or for other reasons.
These days, the more obvious the post-production trickery applied to a photo, the more obvious (to viewers) that trickery has been employed and, generally, the less able they are to suspend disbelief. (Like most rules of photography, this rule isn't etched in stone.)
For the most part, we see the results of shooters attempting to convince viewers to suspend disbelief through their use of post-production techniques. But there's a point where many viewers will refuse to suspend their sense of disbelief. Often enough, when a photographer has gone beyond that point, their work is criticized or questioned or worse.
Unfortunately, there is not a hard-and-fast rule that points to the line where suspension of disbelief becomes nearly impossible for most viewers. Photographers need to apply their own discriminatory and aesthetic abilities to determine that line or whether the line even exists given the general subject of the image.
Does the model's skin look nearly flawless yet still believable? Or, does she look like she's coated with some sort of poly vinyl material?
Is the model's shape truly near perfect? Or, has she been liquefied, modified, and unreal-ified to the point that viewers simply don't buy it?
Those are the kinds of questions and more you should be asking yourself as you are processing skin or making waists smaller and tits bigger or performing other manipulations in post.
In some ways, perfection is over-rated. Often, viewer's won't buy into the photo representation of a model that is, simply, way too perfect. Again, there's a point where people will accept those near-perfect aesthetics and there's a point where they won't. You need to figure out where those points are. Quite often, people who critically appraise your work will tell you, either straight-up or in more subtle ways, whether your work is believable.
Sometimes, it's a good idea to listen to them... whomever they might be.
The gratuitous pretty girl at the top is Chloe from last year. Very little processing performed on the image. Not much suspension of disbelief required. What you see is what she is: Pretty, friendly, with a nice shape and a natural, if slightly mischievous, smile.