Here's what happened. Normally, when we specify a pattern, that pattern matches one or more files on the underlying filesystem, and bash replaces the pattern with a space-separated list of all matching objects. However, when the pattern doesn't produce any matches, bash leaves the argument, wildcards and all, as is. So when "ls" can't find the file /usr/bin/asdf*jkl, it gives an error. The operative rule here is that glob patterns are expanded only if they match objects in the filesystem.