Topic summary
Headrest
Extracted from the Wikipedia article Head restraint.
Reason for discomfort
Headrests are uncomfortable when they push the head forward. In such case there is effectively no gap behind the head and the headrest, or more technically, there's a 'negative' backset (or gap) as the headrest interferes with their natural neutral posture. Data shows that 16% of the population will experience headrest discomfort because of this issue. The rest of the population experiences no discomfort because there is no contact with the headrest, i.e. there is a gap between the head and headrest.