Organon §252

In chronic cases that do not improve with homeopathic treatment, look for an obstacle to cure. 

But if [apart from these cases involving medicines with reciprocal actions] one finds, in a case of chronic disease, that the best homeopathically selected medicine, given in the appropriate (smallest) dose, does not promote improvement, then this is a certain sign that the cause maintaining the disease still persists. Some circumstance is to be found in the regimen or the environment of the patient which must be gotten rid of if the cure is to permanently come to pass.