That can be true, but how many posts have you seen where known defective designs (e.g. "you do not need a MAX232") have been touted as good because they work" ..... If you have a bipolar 12-volt supply available, it's pretty easy to get by without a MAX232 or the like.

Of course I am not referring to 12V solutions, the reference is to the frequently stated 5V only "solution". Typically it show up as "I have a new PC and the serial does not work, since it worked with my old PC it can not be my circuit that is faulty"

Anyhow, the "This works because it is tested" is quite frequent, you see it often in cases where unique timing coincidences are required to show the fault and, invariably the statement is "this is tested, that can not be it". Also, the "tested" does show up in "it works on the bench, but not at the machine"

Erik