I'm loving the St John's Ambulance First Aid campaign for exactly that reason. Using shock tactics for the sake of it or being controversial just to get a reaction aren't the most successful ways to endear audiences to our cause but confounding expectations is something different altogether.
This advert builds on our experiences and expectations based on the type of cancer-related films we often see on TV - and does it very well in my opinion. But then the twist is that this is nothing to do with cancer causes but everything to do with the fact that with just a little first aid knowledge, we could all help to prevent as many accidental deaths in the UK each year as are caused by cancer.
The technique of incorporating a story or media we already know into another piece is often known as inter-contextuality ie; using a reference point that the viewer or reader can relate to from perhaps a completely different genre, to set a scene or make a point without having to explain it. It's why we see so many references to things like Star Wars in other books and TV programmes or why soap operas will use real political or sporting stories to help create credible plot lines.
I think that using the technique in a charity advert is all about putting us, the viewer, into a place where we think we know what's coming up; where we're familiar with the context. Only then to hit us with something we most likely did not know and almost certainly didn't expect. And without (again only in my opinion) being overtly gratuitous or guilt-laden about it.
Given the preamble of the advert, I'm hoping viewers will actually watch enough of it to get to 'the twist' and not dismiss it as a ubiquitous cancer charity advert. I do however suspect that more folks will watch it via viral means simply because it will have the reputation of confounding those expectations and will be shared by viewers as a result. Now, it's been a long time since my Scouts first aid badge, so I'd better think about refreshing my knowledge!
Cap doff to Craig Linton (@FRdetective) for drawing my attention to the campaign - thanks