I'd go further and say it's dangerously untrue. What I advise people is that your results are constantly decaying. Only a rate of progress that exceeds the rate of decay will get you out the door. Decay happens for a number of reasons:

* Your records are never good enough to completely replace your memory of what you did. The longer it takes, the more studies, readings, etc., that you will have to repeat.

* In physical and biological sciences, equipment breaks down, gets taken away, facilities get moved, etc. This stuff happens at a constant rate, and is a pure time cost.

* Technological progress gradually raises the bar for the minimum quality of some results, e.g., in computation. Even "theory" is highly computational these days.

There are also risks of career-ending accidents that can be treated as a constant risk per unit time:

* Your advisor dies, retires, gets promoted to administration, loses funding, changes jobs, gets embroiled in ethical / legal issues, etc.

* Some unexpected new result from another team or industry erases the relevance or novelty of your work.

* You get sick, have family crisis, etc.

* Burnout

Results are the wrong unit of measure. A better KPI is results per unit time. The people who look like they fucked around for 4 years then submitted a brilliant thesis were either working hard all along, or were just brilliant, which I certainly wasn't.

My then-fiancee and I were both grad students. We made a pact to meet at 7:00 every morning in the cafe across from the research building for coffee, to force both of us to stay on a work schedule.

He is obviously talking about computer science. Yes, I know in biology or medicine you can often only access the experimental devices during set hours and the lab may not be accessible 24/7 etc. But in computer science the schedule is mostly free, except for meetings and teaching duties but those are specific time slots not a regular clock-in clock-out job like a cashier or bus driver.

In my part of the world (central Europe), the vast majority of PhD-students is actually employed by the university they aim to obtain the PhD from. So in addition to working on your thesis you most likely have to support other research projects as well as do a lot of teaching. The model of a free PhD student certainly exists, but it is rare.