Full Idea
A disposition which would straight away vanish if put to the test is called 'finkish'. A finkishly fragile thing is fragile so long as it is not struck. But if it were struck, it would straight away cease to be fragile, and it would not break.
Clarification
A 'fink' is a worker planted by the bosses to undermine a strike!
Gist of Idea
A 'finkish' disposition is real, but disappears when the stimulus occurs
Source
David Lewis (Finkish dispositions [1997], I)
Book Reference
Lewis,David: 'Papers in Metaphysics and Epistemology' [CUP 1999], p.134
A Reaction
There are also 'antidotes'. Finks kill the disposition, antidotes kill the effect. These cases are problems for the simple conditional analysis of a disposition - because we never achieved the consequent.