The first and most obvious downside to using the "trial and error" approach in regards to nursing (or, indeed, any medical practice) is that the margin for "error" is so staggeringly large in relation to the trials. Any minor misstep when dealing with matters of health can have disastrous consequences, especially when dealing with people whose health is already compromised. (One must assume that by the time a patient sees a nurse, there is already something demonstrably wrong with them.) "Trial and error" could, for example, lead to a patient being given a medication to which they would have a negative - or even fatal - reaction (warfarin for haemophiliacs, morphine for heroin addicts, etc etc.) A second down-side would be the fact that trial-and-error is only useful in fairly simplistic and fixed-state situations. For example, when wiring a plug, there are only three holes and three wires, and the plug will remain unchanged no matter what happens. Therefore, through a process of trial and error, it should eventually be possible to correctly wire a plug even if one has no knowledge of the theory behind the procedure. A human being is infinitely more complicated and subject to numerous physical and chemical changes, sometimes at a moment's notice. To perhaps over-stretch the metaphor, the plug's blood pressure is unlikely to drop suddenly in the middle of re-wiring.
