Take "choice architecture". This useful phrase describes a powerful phenomenon in human decision-making whereby the context in which choices are presented has a disproportionate effect on the decisions we make. It's important for us to understand since very few purchase decisions involve a straightforward brand "beauty parade". Instead, we make choices within a limited frame of reference, the limits being imposed by, among other things, distribution, social norms or by our internal mental map - or by the way the choice is presented.
If you doubt the power of this effect, think of the question: "Still or sparkling, sir?" What could be more innocent? Actually, it is anything but. Contained within is the presumption that normal practice is to order water of one kind or the other. It is a sentence far harder to answer in the negative than "Would you like some water, sir?" or the technically honest but unprofitable: "Would sir care to pay £3.99 for something freely available from a tap?" The very existence of two alternatives within a category changes the frame, and hence affects consumption of that category. In this case, upwards.
But you are also freezing out possible alternatives. In the same way, the question "Tea or coffee?" contains within it the implicit threat: "Don't get any fancy ideas about Bovril now, will you." Again, a trivial dual choice serves to reduce choice overall.
A worse example is found in the alcoholic drinks category. Kingsley Amis called "red or white?" the most depressing three words in the English language. I see what he means. Because what those three words say is: "At this ISBA reception (or similar), I am offering you no choice over what you drink - you can't have gin, whisky, rum or a Bacardi Breezer and if you don't want to appear rude, you won't ask - but by offering you an entirely irrelevant choice between bad white and bad red, I am closing down your preferences."
If I were Diageo or Pernod Ricard, I would invest millions in trying to solve this. Most Celts like me, frankly, would much rather drink spirits - and wine is a ludicrously overrated drink, with an absurd inconsistency in quality.
But perhaps wine is not the worst example of a bogus duality distracting us from proper contemplation of possible alternatives. Perhaps "state or private?" is a bifurcated choice distracting us from more important questions - namely what kind of education and healthcare systems we really want.