“We had to let him go” is a sentence with a trick in it. “Let” implies permission. It suggests the employee was straining toward the door and the company, reluctantly, stopped holding him back. In reality he was sitting at his desk when it happened.

The grammar tells you who the word is for. “I fired him” has an actor. “He was let go” has a passive voice and a verb of release. Nobody did anything; a grip loosened.

Mamet’s theatre test is useful here. Put the line in a play: a boss says “we decided to let you go” and the audience hears, instantly, a man who cannot say what he is doing. That is the gap the essay is about. In a play it is a character note. In an office it is just Tuesday.