From personal experience, if I didn't get enough sleep or haven't eaten well, the productivity of my work just go down the drain. I get cranky and I can't focus

From personal experience, if I didn't get enough sleep or haven't eaten well, the productivity of my work just go down the drain. I get cranky and I can't focus, but I have seen a lot of engineers who can work for days sleeping just few hours a day on just crackers. They don't mind not eating or sleeping well as long as they meet the deadline.