The point of this question is that when asset prices are declining banks become disinclined to lend and people also become disinclined to borrow to invest. This is an aspect of deflation that can rapidly deteriorate into a deflationary spiral.
So during such rare deflationary environments, like during 2008 and what appears likely again over coming years, even a ZIRP with banks paying negative rates will not force banks to lend nor investors to borrow.
