What is gettier's guy in barcelona thought experiment?

Gettier's paper used counterexamples to argue that there are cases of beliefs that are both true and justified-therefore satisfying all three conditions for knowledge on the JTB account-but that do not appear to be genuine cases of knowledge. Gettier, therefore, argued that his counterexamples show that the JTB account of knowledge is false-and thus, that a different conceptual analysis is needed to correctly track what we mean by "knowledge".