>When you're talking to people you live with it is true that they know which store you are going to.
replyBut again, people use this even when I have no reason to know which store they went to.
I’m not necessarily saying they should stop doing this, but it’s clearly not the usual kind of definiteness implied but the use of “the”.
It is common for someone to say, for instance, "I need to go to the store" even if they don't have any particular store in mind.
replyA prescriptivist pedant might insist that this is incorrect, and they should instead say "I need to go to a store", but in my judgment as a native speaker, the version with "the" is more idiomatic, and the version with "a" sounds stilted.