Miller(1956) put forward that human brains could only process information up to 7±2 chunks,which was called Miller's rule.Although the actual magic number implied by the rule is still in dispute in academics,it is widely recognized that human brains have capacity limits in immediate memory and information processing.According to Miller's rule,people will face a constraint in number of items to process,which may exert significant influence on consumers' ordering of consuming goods bundles.This paper,based on a simple two-staged experiment,proves that preference ordering beyond the processing capacity of human brains is unstable.Miller's rule and our experiment indicate that consumers' perference on goods bundles are usually incomplete.Due to processing capacity limits of human brains,consumers could only report stable preference ordering.This is also the reason for many found yet unexplained economic phenomenon.Miller's rule should have greater development and applications in behavioral economics.