This is a standard PROLOG predicate. It never succeeds, thus causes backtracking to start. Fail may be used to program endless loops, or in combination with ' ! (cut) ' causes a predicate to definitely fail.
member(X,[a,b,c]), write(X),nl, fail.
member(X,[a,b,c,ende,d,e]), write(X),nl, X = ende,!,fail.
No runtime errors.
prolog-process, client-server, object
! , true