I know, yet I have no idea how people get it so wrong. I mean apart from anything else there is usually a nice big label to tell you want to put in it in most modern cars...but even that shouldn't be needed on people's own cars ...I can understand it on a hire/courtesy car though ...especially as some of the very new 4 cylinder petrol engines now sound amazingly like diesels.
Innattention basically, there is a very large percentage of the population who just have no ability or desire to pay attention to what they are doing, some of the stuff that happens on our forecourt is frankly shocking, you end up wishing that the Police had a permanent presence and had the power to ban people on the spot.