This was expressed quite emphatically, in exactly those terms. Emphatically and, sadly, quite publicly. Not sad for me - sad for the individual raising the objection. I'm afraid he didn't boost his credibility much...
Naturally, this assertion of FIST's impossibility came as a surprise to me, since a) I've done it several times and b) I'd just spent 30 minutes telling stories about other people who have also done it. Undeterred by these stories, testimonies and examples, the gentleman stood his ground. FIST can't be done. Hmmm...
Now, my first impulse was to suggest that "the person who says a thing can't be done should never interrupt the one who's doing it." (not sure on the source of that quote) But that wouldn't have been polite & respectful, so I demurred.
Instead, I said something along the lines of "Well, you're free to not try to do things this way if you don't believe it's effective, but it's something I'm going to continue doing..." And then I continued with my presentation.
In retrospect, that wasn't a great answer. What I should have done was acknowledge that this individual had apparently encountered a situation where the FIST approach did not work (possibly because it wasn't tried?). And then I should have suggested that the existence of a situation where things weren't FISTy doesn't prove there is no situation where FIST can be effective. There's really no reason to globalize failures. Sort of gets back to the whole question of data & how we interpret it.
One data point can disprove a negative (i.e. I propose A doesn't exist. Someone finds one A and my proposition is disproved). But one data point can't disprove everything (i.e. I propose A can be done. Someone finds a situation where A is not done - the proposition is not disproved).
Fortunately, several other audience members chimed in and helped address this gentleman's concerns. I'm not sure he was convinced, but it was good to see that many other audience members understood what I was proposing.
The truth is, I kind of liked the way things worked out. Sure, it would have been better to have someone raise a substantive & thoughtful objection, but even the "this can't be done" comment triggered something in the audience that I, the speaker, couldn't do directly. It engaged them and got them to express their understanding of the concept. Can't really ask for anything more than that.
I think I owe that guy a thank you.