These things happen to one level becomes the subject, stimulant. People will learn how to deal with the historical experience from stimulating things. Make him know you'll respond and how incentive.
These things happen to some degree, it becomes a stimulus. People will learn how to deal with stimuli from past experience. He knew how to respond to stimuli.
These things happen to a certain level will become the trigger. People will learn how to deal with the incentive from the experience in the past. He knows how to respond to stimuli.