It's about confusing correlation with causation.
Look at Cargo Cult Agile for example. Company X is very successful. Company X uses points to estimate tasks. Therefore, if we use points to estimate tasks, we will be successful.
Remember when everybody went crazy for Erlang because WhatsApp was written in Erlang?
Wikipedia actually has an article on "Cargo cult programming". They have it as "the ritual inclusion of code or program structures that serve no real purpose".
> Surely if you don't get the result, you try something else.
Results have many "dimensions" and it is often not clear what THE result is. You will usually get A result though.
EDIT: ah right. So you 'may' get the result, but it's not due to the thing you have ascribed it to.