There is a popular argument amongst creationists and even some other Christians that goes something like this: "stuff in our world just works, therefore it must have been designed by a powerful, intelligent designer." It's similar to both the watchmaker argument and the banana fallacy, but not exactly; this one relies less on the complexity of the "design" or the human-centric nature of it, and more on the flawless operation of it.
Perhaps the most infamous proponent of the argument was Bill O'Rielly, with his "tide goes in, tide goes out" bit (starting at 1:50 below):
Not all tellings are necessarily as amusing as Bill's, but, if you discuss humankind's beginnings with religious people, it is bound to come up.
The "tide comes in, tide goes out. Never a miscommunication" argument (or, what I call the "shit works, therefore god" line) gets it exactly backwards, though. First, it overstates the quality of the "design". Nature is awash with "miscommunications", when the optimal working order of a thing or being is, through some natural process or mutation, turned on its head. If a lack of error is evidence of God, we have no such evidence of God; amongst our own species, people routinely suffer from genetic defects and "miscommunications" that oftentimes greatly impair and even kill us. Heart flaws, genetic illnesses, etc., can surely be viewed as aberrations of an ideal human design; and yet they are to be found all over. The same is true of other species of animal, of vegetation, etc. We have good examples of what perfect working models are, but that is not a state shared or retained by all. So the alleged perfection of what is claimed to be God's design is simply bollocks; "miscommunications" happen constantly. If an absence of them is evidence of God, we can at least conclude that we have no such evidence.
On the other hand, a state of reality like our own, complete with errors, is very much in line with natural selection. Flaws of a nature not severe enough to ensure extinction can (and do) exist in a species, but errors of a sufficiently weighty nature to increase the chances of extinction are not generally passed on -- particularly in more difficult times. This is true wherever you look. A plant susceptible to blight is less likely to survive long enough to reproduce, a deaf lion will be less likely to pick up on sounds of consequence to his survival and reproduction, etc. Even something as simple as bad eyesight, in more dangerous times, would have been a significant handicap; the individual with poor vision would be less likely to spot danger, and more likely to die before the genes for it could be passed on. Nowadays, stabler societies and increased technology have relegated this to a minor concern, and so we "four eyes" don't have much to worry about in that regard. While it's still a disadvantage, a defect even in terms of design, it doesn't threaten our own, or -- as it proliferates -- the species', survival; what is a flaw in "design" survives natural selection. So it is with many medical ailments of a more serious nature as well. Nowadays, we can treat formerly fatal conditions -- not because we have corrected a design flaw*, but because we have enhanced our own survivability in the process of natural selection. And this process continues to get better, as our species advances; we are a social species, and we strive to augment the more narrow constructs of survivability that the natural world imposes. We see the effects of this every day -- people in some parts of the world live long, healthy lives despite conditions or circumstances that would kill people in parts of the world where that social instinct has been negated by poverty or warfare. So when we look at a part of the world where the vast majority of people exist in a state of relative survivability -- but a far cry from the perfection of a flawless design by a perfect and all-knowing creator-designer -- we are seeing the results of natural selection: an intelligent species that has advanced beyond the most basic survival, to a point where it can tweak nature sufficiently to boost the survival of its fellow creatures. That is what we would expect from the process of natural selection on such a species as ours; but it is certainly not what you would expect from an intelligent designer.
In conclusion, "it just works" is wrong because it ignores the ample instances where systems, organs, etc., don't work as per the general use; furthermore, such an argument entirely disregards the fact that natural selection would both ensure that in most cases only that which works well enough for a species' survivability gets passed on to future generations, as well as account for the presence of what can only be construed as design flaws and workmanship errors in a designed/created system. Natural selection is a not only a far better explanation that intelligent design to fit the reality of our world, but it actually makes sense.
* I should note that I do not use the terms flaw and defect in a pejorative fashion, to imply that there is actually something "wrong" with individuals; I simply mean that, from the standpoint of a grand designer, these would be seen as defects in workmanship, flaws as it were, aberrations from the gold standard of perfection. My argument is that nature is far more complex than that, and that the design argument is foolishness; not that those who would fall into the designer's category of imperfection are actually imperfect. I should note, I am one such; and, I would suppose, most are (those rare people who have no physical, mental or social deficits, no
propensity to illness, no weaknesses of any sort, absolutely no need of medicine or healing, being the exception;
and if they were many, I cannot but think the rest of us would long ago
have been rendered obsolete). There is no design, thus no gold standard against which to be judged perfect or imperfect. There are optimal states, but we are, all of us, through our own human ingenuity and through our genes, survivors of natural selection, fitting within the range of survivability that allows us to be here, now. We don't have to find a place in the stark dichotomy of perfectly created or imperfectly created. The broad range of "good enough, thank you very much" that natural selection allows for, and that we continue to expand, is what most of us fit into...