People on average are only productive for 3 hours a day

I was reading some stuff and I found this https://www.inc.com/melanie-curtin/in-an-8-hour-day-the-average-worker-is-productive-for-this-many-hours.html Do you agree with this? to the people working on an office environment, are you productive for the whole 8 hours or is true like in the article that you're actually only productive in 3 hours. I wanna hear your experiences

never worked in an office but i guess effort does tend to wain when there's like an hour left of work, but I'm on my feet, so maybe that's why?

Makes sense. Way back when, humans didn't really "work" much more than a few hours a day. Gotta conserve energy between meals. While our jobs/careers/hobbies may have changed, our biology hasn't. Not to mention,as dumb as humanity may seem at times, we're really good at finding shortcuts so we don't have to work for a long time. So, is being productive for an 8hr shift and getting your job done any more productive than getting it done in half the time and chilling for the rest?

The study is based on 2k people so it would be interesting to know what kind of jobs were sampled by percentages of the group like if it calls for a load of paperwork or communications with people outside of the company, their locations (smaller cities or metros), .... just more in depth. Quality of work also didn't appear to be a factor, only the amount and time accomplished. Meh