K.I.S.S. my ass.
Nonetheless, the thing about K.I.S.S. and parsimony is that you have to be very careful that you don't get so focused on the "simple" that you forget the "solution." In engineering or in science a solution is meant to deal with some particular problem and, while simple is good, a straightforward approach that doesn't fix the problem is not preferred over a somewhat more complex approach that does fix the problem. K.I.S.S. and parsimony are really only good standards for judging between solutions that are equally good at dealing with problems or, at the very least, very close to equally good. I bring this up because people very frequently take a preference for simplicity to extreme lengths, and often end up paying a price for it.
To understand what I mean, consider this comic from the excellent xkcd:
Humorous as this may be, it depicts a process that is familiar to any student of social psychology and, particularly, someone conversant*** with Status Characteristics Theory. This theory, for those who don't know, deals with how certain traits increase or decrease our rank within social groups. A characteristic (e.g. skin color, sex, age, training, habit, etc.) that influences one's rank is said to confer status and, so, is a status characteristic. Particularly, status characteristics come in two different flavors: diffuse and specific. A diffuse status characteristic is one that impacts your rank in a wide variety of different circumstances whereas a specific status characteristic only influences your rank in a limited set. So, being white in the American southeast**** can be thought of as a diffuse status characteristic because it boosts one's rank in a variety of situations, whereas being an electrician will only boost status in situations dealing with electricity and wiring. Additionally, diffuse status characteristics are often easily observed while specific status is harder to see. So, you know within seconds of meeting me if I'm male or female, white or black, but it probably takes you longer to figure out if I'm good with computers or handy with a hacksaw.
What's interesting is that because diffuse status characteristics have such a broad influence, they often cause us to assume incorrectly that a person will be good at a given task. So, I sometimes get to read over on Uncommon Descent about an engineer or computer programmer who doubts evolution. This is fine but, the thing is, what do either of these occupations have to do with evolutionary biology? Well, nothing. Being either indicates that the person is pretty well educated, and education is a diffuse status characteristic, but engineering and computer programming do not confer any particular expertise in evaluating biological science. Yet, because education serves as a diffuse status characteristic, the doubts of these folks are supposed to be convincing in and of themselves.*****
And, in the above comic, we can see this same process playing out. You see, studies suggest that sex serves as a diffuse status characteristic in which (surprise surprise!) maleness is more valued than femaleness. As such, in interactions males are given a disproportionate share of attention, of credit, and of deference. The thing is, the same process can also work in apportioning blame. When one male discovers that another male is bad at math he makes an attribution about the cause, asserting "You suck at math." This is okay- it's a claim about the level of a specific status characteristic. When a female makes the same error, however, the diffuse status characteristic comes into play and he asserts that "Girls suck at math." Because femaleness is thought to be less valuable than maleness, the observation that a specific female is bad at a thing reinforces the original belief that femaleness is bad. Because one female is bad at math all females are now taken as being bad at math. On the other hand, because maleness is valued the observation that a specific male is bad at something is just cause to conclude that a specific male is bad at something. It's a version of that old favorite game, "Heads I win, tails you lose," and it helps to explain why status orders are so gosh darned resistant to change.
And this, unfortunately, has a lot to do with K.I.S.S. Diffuse status characteristics are convenient ways to make guesses about the competence of others but they provide no certainty. So, if you encounter someone who has the low value of a diffuse status characteristic, and who is poor at some task, it's easy to explain the one with reference to the other. It is, in effect, a nice simple explanation. But, as we've figured out by now, simple is sometimes just another word for wrong. It's good to keep things simple, but not so much so that our solutions don't work anymore.
Perhaps in the end the most important lesson of all is that our judgments of other people may simply be wrong.
* I once worked for a man who had a certain amount of difficulty with this acronym, explaining it as, "Keep It Stupidly Simple." If you're familiar with the English language you have already realized that this entirely changes the meaning. Oddly, however, he inadvertently hit on a better way to describe our products. Ah, serendipity.
** And I don't mean the hammer.
*** I refer here to my wife. The most complicated thing I'm conversant with is putting my pants on in the morning.
**** Not to mention a wide variety of other places in the United States.
***** Note that I don't object to these folks having opinions, or even disagreeing with established authorities. I just disagree with their educational credentials being used to lend credibility to those doubts. Hell, I'm educated, I believe in evolution, but I don't think that it's legitimate to try to convince someone by saying, "I almost have a Ph.D. in Sociology so you can trust me about quantum physics!"