If we contextualise thoughts with the physical senses (mind can be considered the sense of thought), we can see when discomfort is felt how the mind reacts with psychological aversion. That aversion manifests as a new sensation, bodily tension or what have you, to which the mind again psychologically reacts, feels, reacts, feels, in a loop. Thus, it is not thought itself that causes other thoughts, but an interface at which mind becomes matter and matter becomes mind.