[JustinCS]

This isn't really true, everyone has a different basal metabolic rate, and effectiveness with absorbing calories from food can vary as well. Even small differences can add up to large effects, the difference between being at net-zero, or having caloric surplus or deficit every day.

That said, in practice it may be reasonable advice on average, but there's also a problem where it's not very practical to eat the "same" calories as someone else, unless they are together with you all the time.

[Arisaka1]

As someone with fast metabolism who struggled to gain weight: I get that, but at the same time, understanding that there's trial and error with your own body but is ultimately all about input and output does more good than saying "haha I just have fast/slow rate looool" as justification for not taking care of yourself.