The case below teaches us both that quality and quantity matter.  We may be very correct in our diagnosis and formula choice yet get it wrong in terms of the dosages of the individual herbs.  Often practitioners are afraid of the action of an herb and so radically reduce its recommended dosage in a formula.  Yet, this shift in dose can completely change or eliminate the effectiveness of the formula.  How can we be safe when we are cutting ourselves off from the healing power of a formula?  Having a patients illness continue is also far from being safe.  If we are afraid of an herb and so change the basic structure of a formula by using way less than Zhong Jing advised, we can get very poor results.  Below is an illustrative case I found:  

俞妖荣 Yu Yao-rong wrote in his《伤寒论汇要分析》Compiled Analysis of the Shang Han Lun:

A friend had slight cold with fever, dizziness, and discomfort and fullness of the chest and rib-side.  This had gone on for many days with no cure.  He diagnosed himself with a Shao Yang illness and gave himself Xiao Chai Hu Tang.  However, the Chai Hu he used was crude, silver, Chai Hu.  This didn’t work.  Then he used 8 fen of Bei Chai Hu, gradually increasing the dose to 1 fen.  He took several packages but the symptoms continued.  Without a doubt, this was a Shao Yang pattern, so why was Xiao Chai Hu Tang ineffective? Although this was not a serious disease, it had been persistent for many days and my friend was quite worried.  One day he came to talk to me.  I said that Master Zhong established Xiao Chai Hu Tang.  In his original formula, Chai Hu is used in a dose that is three times that of Ren Shen.  You use half the amount of Chai Hu relative to the other herbs.  But, this is using it as if it is an assistant herb in the formula!  How then can it dispel the cold and heat and resolve the half interior/half exterior evil?  He asked me how much Chai Hu he should use.  I told him to use 3 qian.  He laughed, saying that he would rather suffer more days than risk this great danger.  I spoke to him sternly saying “  Can’t you see that you are being chased by ghosts?”  He became silent.  He then started to use Bei Chai Hu in the dose of 2 qian and he was cured.