I blogged previously that a key maxim that medical students should have branded into their brains is "Every one does not react in the same way to treatment".
There is more to it than that. Everyone with the same illnesses does not present in the same way,everyone with same illness does not always have the same results on lab tests or imaging and everyone does not accept a physician's recommendation in the same way.
I came across a memorable quote that captures all of that in an eloquent way and needs to be appended to the hypothetical handout for med students of the very important Milbank Quarterly article by RL Kravitz which is entitled "Evidence-based medicine;heterogeneity of treatment effects and the trouble with averages"
The author is Dr. Leon Eisenberg,the reference "Medicine-Molecular,Monetary, or More than Both", JAMA july 26,1995-vol 272, no. 4 p 331" While I do not agree with all he said the following is dynamite"
"...Medicine deals with phenotypes,not genotypes. Between genotype and phenotype, a lifetime of individual experience has fashioned what began as an envelope of stochastic probabilities into a singular personal embodiment: the patient who faces us.
In clinical practice, it is the particularities and idiosyncrasies of the individual patient that challenge the physician. The same disease never presents in quite the same way in successive patients.
Complaints vary: severity varies, response to treatment varies. Nondisease, that is, nonorganic disease, mimics "real disease" with remarkable fidelity"
In short, there is heterogeniety of almost everything and possibly why Hippocrates noted that experience was treacherous along with judgment being difficult.