I don't think leetcode problems are a good example. But I have worked (programmed) two 9h days without sleeping in-between before and it worked somehow well???

I don't think leetcode problems are a good example. But I have worked (programmed) two 9h days without sleeping in-between before and it worked somehow well??? Through normally I often have problems working 8h a day without taking a fairly long lunch brake. But then sometimes I just went 10h with close to no brakes (some ad-hock food) without even realizing it. It's still puzzles me what makes the difference.