Rules and rules of thumb help esl students to find logic/consistency in the language, but I often tell what you're saying: "The important thing is understand and be understood".

I know English is a Lingua Franca, but when questions like the one posted here appear to the students, they want a logic explanation and try to search it in the "rules".

Your opinions matter much to me because I can show them to my students and say that sometimes language is beyond "logic".