7 is enough for a lot of adults. especially 7 hours of quality sleep. After seeing a sleep doctor I realized that stressing out about not getting exactly 8 hours each night was part of my problem! I did a lot of experimentation to find my optimal hours and it was not quite 8. Trying to force extra hours doesn't really work.

That's what my wife and I sleep for, 7 hours. 8 and we wake up with a headache.

AFAIK 7-9 hours is the commonly used range, anything less than 7 hours or anything more than 9 can have detrimental effects on how well rested you feel after waking up. Where did you get the notion that adults need exactly 8 hours on the dot?