Instinctively you would think that the lower the number of elements in an activity, the lower the complexity. Not necessarily so. It is often the case that an activity with just three, four or five elements can be fiendishly complex. I'll call this the Complexity of Simplicity.
CoS is most apparent when making food recipes with just a few ingredients. Scones, shortbread, hollandaise sauce, macaroons, tablet, puff pastry and soufflé are some example dishes, with just a few ingredients, that are really hard to get just right. I'm not saying that it is impossible to produce a, for example, hollandaise sauce but it is really hard to make a great one and to do it consistently.
Small variations in temperature, humidity, quality of ingredients or technique can render an otherwise acceptable dish completely unsatisfactory. As these dishes have very few ingredients even small changes have a disproportionate effect on the quality of the finished product. Bread is another example. A simple loaf may only have four or five ingredients but the way you deal with them can have a huge impact. Prove too long, don't knead enough, add too much water, oven too hot, not score deeply enough; the list can be endless.
CoS also explains why there are national competitions for the best: Scotch pie, shortbread, porridge, scones, tablet, etc. To make the best examples of these dishes usually takes years of practice and high levels of skill.
A simple loaf may only contain: wheat flour, water, yeast and salt, yet the number of ways it can go wrong are almost limitless.
Conversely, making seemingly complex dishes with lots of ingredients can be, if not easy at least, straightforward. A dish with a large number of ingredients often isn't so reliant on you getting the technique exactly right. Sometimes, it is even possible to completely omit one or two ingredients, without greatly affecting the end result. I have often embarked on making a curry, only to find that one of the required spices isn't on the shelf. Usually, if there are several other spices in the recipe, I just go ahead and make the meal anyway as I'll probably get away with it. If something has only three, four or five ingredients you cannot do that.
I have given this subject some thought recently as I am about to embark on a journey of discovery as I make sauerkraut for the first time. Sauerkraut might be one of the ultimate CoS dishes as it only has two ingredients: cabbage and salt. Wish me luck.