It's not really. Do you think I should post a diagram which might not be correct?
Probably not, and certainly not without pointing out that it may not be correct.
As you imply, an awful lot depends upon how much information we are given (including piccies etc.). If we have been given sufficient information that we are pretty certain that we fully understand the situation, then I personally don't think there is a major problem with telling an OP 'which wire to put in which hole'.
When there is uncertainty, things are much more difficult. In terms of light switches, provided that there are no neutrals around (i.e. the common situation with one or two cables, all live cores of which are connected to switch(es), there is no harm to be done (to either people or equipment) - so that, if one can be sure that such is the situation, giving advice from afar which some might regard as 'trial and error' is, in my opinion, not necessarily all that unthinkable. Other situations can be more complication and/or difficult.
It's not unique to 'remote' advice about DIY electrics. Even the care provided by our NHS is partially moving towards a situation in which, in some cases, people are being told 'what to do' (comparable with 'put this wire into this hole') over the phone (or by other means of communication) by people who have received only limited (and not necessarily always correct) information provided by the person concerned (who obviously 'does not know what to do', since they're asking, and do not have the time or ability to go to Medical School in order to find out the answer to their immediate problem for themselves!). Just as with 'you need an electrician', they have the option of 'you need a GP/hospital/ambulance' - but they by no means always invoke that.
Kind Regards, John