You need 8 hours and 36 minutes of sleep for optimal performance

From the Wall Street Journal:

One of the most influential studies of human performance, conducted by professor K. Anders Ericsson, found that top performers slept 8 hours and 36 minutes per day. The average American, for comparison, gets just 6 hours and 51 minutes of sleep on weeknights.

You are simply a different person when you operate on insufficient sleep. And it shows. If you do not get enough sleep, it can lead to a cascade of negative events. You achieve less at work, skip regular exercise, and eat poorly.