They were; I just picked that as a convenient example of a non-reversible idea. Once you dump the iron in, you're committed. It turns out that in a dynamic system (ahem) that just smashing one of the inputs doesn't guarantee a linear response, but regardless, you're committed once you've done it.

(It turns out that in this case the system tends towards stability. There are good reasons to believe that most changes we can make will also be neutralized. But there's no a priori reason that the same experiment couldn't have experienced a wildly disproportionally large response instead.)