Why 8 hour timing is necessary for any job?

It has been examined and tested by different means that human being can give his best in the job up to8 hours. And24 hours in a day has been scientifically has been divided into different purposes, like own private activities, rest/sleep, and work. Universally,8 hours are accepted to work and that’s why anyone is working beyond8 hours is paid extra remuneration/ benefits by the employer.

its Not.... but its according to Labor rules ...