"A sorry costs nothing"

You'd say, even granting the trade, that a sorry is a small thing and there's no limit on them. You can issue as many as you like. Nobody runs out.

Roy Lewicki and colleagues, in 2016, studied what makes an apology work. They identified six components from earlier research, acknowledging responsibility, explaining what went wrong, expressing regret, declaring that you'll do better, offering to repair the harm, and asking for forgiveness, and tested them singly and in combination. Apologies with more components were judged more effective than those with fewer, and some components mattered more than others. Acknowledging responsibility mattered most. Asking for forgiveness mattered least. An apology, in other words, is a structured thing, and it works because of what's in it, and a bare "sorry" is the smallest unit of it.

Now think about what the reflex sorry does to that structure. It takes the smallest unit, the one word, and issues it forty times a day for things that had no responsibility to acknowledge, no harm to repair and no regret to express. A currency printed too often is a fair comparison for two sentences. Each note is still a note, and none of them buys what it used to.

Here's the cost, and it's the one that convinces most people. When you've actually done something wrong, forgotten the thing, snapped at someone, let a friend down, the word you reach for is the one you've said forty times today about doorways. The listener has heard you say it about the rain and the cold and the fact that you asked a question, and now you're saying it about a real fault, and it sounds the same. It has to. It's the same word from the same person in the same tone, and the listener can't tell the real sorry from the reflex one, because you've spent years teaching them that your sorry means nothing in particular.

So the reflex sorry does cost something, and what it costs is the real one. A person who saves the word for faults has a word that means fault. A person who says it for weather has a word that means weather, and when the fault comes, the word for it has already been used up.