The way it works has nothing to do with what's "evident" to whom, nor according to whom.
It's linguistic, not philosophical.
An indefinite article is used the first time an object is referred to in a discourse.
After that, the definite article is used for subsequent references to the object in the discourse.
Referents become "definite", in other words, by being already loaded in working memory.
Until they're retrieved from storage, they're "indefinite".
This is the general rule only, understand; it is frequently superseded by literally dozens of other, specialized, individual, idiomatic rules for the use of articles.