We always leave something as we are moving about.
Every time we enter a room traces of fibre from our clothes are left where we stand and walk.
If a person has been sitting in a chair dressed in a sweater, fibres from this sweater will stay on the chair and fibres from the chair will stay on the sweater.
Looking for these kind of traces in a crime case, you will first tape the whole sweater and then the chair with an adhesive tape. If a match is found there is evidence that the two elements have been in contact.