I'm afraid it's the unhealthy penchant for dodgy prepositions, plus a genuine love of the French language and a desire to understand it properly. I do do some tuition, mostly young children and adult beginners, but the adults question points of grammar a great deal, and sometimes it's difficult to give totally satisfactory explanations. I wasn't expecting poetry as a reply to my own query! That was lovely, and I really appreciate the time and trouble you have gone to, Vraititi.