Dear Mogwai
Several reasons
1-the patient has perhaps antidoted himself
2-the wrong 'second' prescription potency its not always the next higher up potency
the vital force is tricky-it only resonates with certain potencies not all.
3-There might be a block-this could require a nosode
after the block has been removed continue the same remedy once again.
4-perhaps its nOT the well indicated remedy afterall.
Perhaps the immed. results were mere acute suppression and not a true path to cure.
Suppression "often" looks like "its getting better",symptoms are showing relief.(pain is gone,cough is gone...........etc)
A trained practicioner can tell the difference.................

__________________
"Great ideas often recieve violent opposition from mediocre minds"...................Einstein