Because with difficult cases doctors tend to use refelective reasoning for diagnostic decisions. Reflective reasoning is effortful, conscious analysis of features exhibited by a case like during a dog bite incident where you have to act fast to avoid the infection.
When engaged in reflection for solving a case, physicians tend to more carefully consider case findings, search for alternative diagnoses, and examine their own thinking. A recent study indicated that reflective reasoning positively affected diagnoses of complex cases, whereas it made no difference in the diagnosis of simple cases
Nonanalytical thinking is based on the recognition of “illness scripts”. Physicians tend to recognize these patterns of symptoms very easily especially when having more experience. This type of reasoning is very fast but not always accurate. It tends be vulnerable for availability bias. Physicians tend to change to this mode in routine situations.
From recent research we learn that in dealing with a so called difficult patients, the doctor tends switch to mostly reflective reasoning with more time spent on diagnosis. The physician does a more careful analysis of findings and alternative diagnosis. Diagnostic accuracy improves with this type of reasoning in these cases. Moreover, physicians shift to reflective diagnostic reasoning when they perceive the case to be solved as problematic irrespective of whether the particular case is really problematic or not. It is impressive to realize how easily doctors are influenced by circumstances instead of being neutral and objective to each case.
Mamede S, Schmidt HG, Rikers RM, Penaforte JC, & Coelho-Filho JM (2008). Influence of perceived difficulty of cases on physicians’ diagnostic reasoning. Academic medicine : journal of the Association of American Medical Colleges, 83 (12), 1210-6 PMID: 19202502