The thing is that cooking, as it's (usually) based on products that have some intrinsic variability in them ( plants, dead animals... ) hence the recipe cannot be made fully deterministic. I know for gnocchis for example, the amouny of flour needed depends on the moisture content of the potatoes which depend on the variety uses, and how long they've been stored... Also depends on the flour you use. Until you get the dough texture "just right". Agree with many comments here that this makes a cooking an art.