in the method doing trial and error ...
Let us assume that a particular money making method as per reality is doable, rather achievable and some or many people implemented it and are earning money by using that method.
This does not mean that anyone and everyone who tries that method would end up earning money from it, no matter the amount or extent of work put in.
But why so ? Because here is the main aspect, which may attract criticism (but no issues) :-
Not everyone has the same "understanding" or rather comprehension skills & cognitive skills and hence not everyone would be able to correctly implement the method, due to not comprehending rather not understanding the method correctly.
I will hit the nail straight on and say what I exactly mean, many people would disagree (no issues) :-
Just like we all have different physical abilities and capabilities. The same way, we all have different mental & different cognitive abilities.
Depending on our "makeup", for example no matter how hard every one of us work out on building our physical bodies, can all of us become a body builder like how Arnold Schwarzenegger is (or was) ? Obviously no. Inspite of best efforts each one of us will achieve various different maximum level individually.
The same way, even in mental or cognitive related "building", no matter how much efforts are put in, depending on each person's "makeup", not everyone can have or reach various "levels" mentally or rather cognitively. It will and in reality differs from person to person, no matter how much effort is put in.
Hence not everyone will be able to correctly comprehend a working method in the best way possible, in order to implement it in the best way possible.
The exact same working money making method given to a Mr.A and a Mr.B .... Mr,A may end up earning a lot from it and Mr.B may end up earning zero nothing from it (inspite of working quite hard on the method).