All normal human beings talk. Many find it hard to imagine living without language, so much so that they sometimes fantasize about a world in which animals can speak, as when a character in a children's storybook encountered a chattering toad:

Language, then, is taken for granted. But its nearness and naturalness cause two problems. First, people do not usually spend time observing it. The situation is somewhat like that in a Sherlock Holmes story, in which the fictional detective questioned a visitor about a flight of stairs:

Similarly, language speakers see, but they do not observe. More accurately, they hear, but they do not perceive. Language is all around them, but most are unable to answer even straightforward questions, such as ‘When do children become competent speakers?’ ‘How do language changes happen?’, and so on.

The second problem overlaps with the first. Because everyone talks, many confidently assume that they can therefore pronounce authoritatively on their language.