I have found that recently many answers and comments have been written in a tone suggesting that their answer is an actual grammatical or linguistic rule of English, i.e. something that must or should happen, when in reality it is simply a matter of common usage, i.e. what tends to happen, most of the time.
The cases of usage in this answer (link accessible to who sees deleted posts)
The percentages in this answer and its comments
Don't get me wrong. It is absolutely important to talk about common usage and how words and phrases and grammatical forms tend to be used in everyday conversation. I would even argue that this is just as important for an English language learner as understanding the technical bits of the grammar.
However, with that said, I think it is important that when something is a common usage, not a rule, that is made clear. An ELL likely would not know the difference without it being specified (that's why they're here, to learn the rules they don't know), and this can be confusing and discouraging, especially if they encounter a discrepancy in conversation soon after.
Can we please make an effort as a community to specify when something is a rule and when it is simply common usage?