Agata Plank

There is significant parallels between how he does not touch alcohol EVER starting from Men at Arms and every other ways that he holds himself accountable in the books.

One minute late to storytime with his child would be one minute too much, because once you excuse one minute late then you can excuse five, ten, and then fifteen minutes late. -> one drink is too many drinks because one drink « tends to arrive in five glasses ».

« If you do a bad thing for a good reason you’ll do it for a bad one », « If one part of the machine breaks down it all breaks down » and « who watches the watchman? Me. » are all different ways of saying that Vimes cannot allow himself to make even one exception in how he behaves. Will not, yes, and that’s very admirable, but this will not is the result of a CAN NOT because what would happen if he did is not, in fact, unthinkable. On the contrary, he knows very well what would happen if he did break one of his many rules, and this is exactly why he doesn’t break them.

« One drink is one too many » is basically the center of his character’s moral code. And it hits so hard because he’s not being rigid for the fun of it, he’s like that because he knows. It’s a sliding slope and he’s been on it and at the bottom of it and he KNOWS how quickly it slides.