Just ask how much you weigh. If the pilot hasn't weighed you, or asked how much you (and everyone else) weighs - then they are guessing. Yes - a GA strip with two on board you can guess and be pretty sure you are right.
But a limiting strip? A professional KNOWS. An amateur guesses - and then spends the rest of the time until clearing the trees desperately hoping they are right and haven't killed everyone by stuffing it up.
(The professional does the calculation so often they can whip through it in 30 seconds - the amateur hasn't done one since the PPL exam they cheated on, and knows they would take an hour and a half to get a decent answer.)
Airliners have one of the highest safety records for transport on the planet - and guess what? They run take off distance and weight and balance calculations as a matter of course for EVERY take-off.
The runway discussed may have been suitable. Sometimes it swings the other way and the book says you can do it. Does not mean you actually will be able to do it. Eg in video.
https://www.youtube.com/watch?v=ZmEVwyMRYIY