Case taking is essentially a social interaction between a physician and a patient under certain pre determined condition.
We have to face many difficulties because of the ignorance of the masses who are not accustomed to a detailed narration of their sufferings to enable us for a homoeopathic prescription. our task is made even more difficult by the easy methods adopted by the modern system of medicine.

Bringing the masses, who are accustomed to the easy methods and impressive instruments, to the simple but the surer method of cure is a difficult task. We must under stand that their can be no substitute for human brain and that no instrument can understand  the human sufferings and only a human mind can realize the depth of the sufferings.

1. The influence of modern system upon the people
A physician trained in modern methods of treatment does not trouble the patient much by way of asking questions for case taking. The patient who are accustomed to such procedure and influenced by these techniques, come to a homoeopath and expect him to follow the same procedure with out touching the patient much in the way of interrogation and prescribe medicine for his trouble, yet expecting to have better results.

2. Changed symptom image
When all the possibilities of allopathic medicine including surgery fails, patient come to the homoeopath as their last resort. By the time he must have consumed large quantity of strong drugs continuously for a long time. The already consumed drug must   have produced their own symptoms (drug proving) changing the symptoms image of original disease, thus making the homoeopathic physician incapable of making a radical prescription. 

3. Complex disease
  Allopathic medicines are not prescribed according to the symptom similarity & are repeated quite often and unscientifically; when natural chronic disease are treated with these drugs, they produce their own symptoms (drug disease) and intimately mix with the already existing natural disease and cause complex disease which are very difficult to cure.

4. When pathology progress the signs & symptoms decreases
Many disease such as cancer usually comes on later in life, when childhood matters have been forgotten, they don't remember the past history or family history. Pathological changes have already taken place.
In proportion as the pathology progress ,the signs and symptoms decreases. In the absence of signs and symptoms / totality of symptoms the choice of the medicine is not possible and on pathology alone no prescription can be made.

5. Modesty conceals the facts
There are certain conditions and sufferings which the patient may not like to disclose to the doctor due to modesty or shame. Due to modesty patient conceal the facts and give vague symptoms which make the correct prescription difficult.
Eg. Habitual masturbation
Leucorrhoea in females

6. Pretension modifies the symptoms
Certain patients exaggerate their symptoms, narrate more than they feels. Some patient narrate less than they feels. In certain grave diseases they don’t complain about their sufferings .These are hinder the proper case taking. 

7. Patients accustomed to long sufferings
In chronic disease, the patient get accustomed to their long sufferings and may not feel the necessity of narrating the symptoms with which they have lived for long, which are important for the choice of medicine. They don’t consider that these symptoms have anything to do with the prescription that has to be made for the present trouble.

8. Symptoms appearing periodically are not narrated
Symptoms appearing periodically are important factors, which will help in the selection of medicine. The patient being ignorant of the importance of such symptoms occurring periodically along with the main symptoms may not narrate these while giving their case history.
Eg.Rheumatism during winter
Diarrhoea during rainy season 

9. Alternating symptoms not narrated
Certain symptoms usually alternate with one another. They don’t understand the important of such alternating symptoms; moreover they are not aware of such alternation, thus making the proper prescription impossible. 

10. The long sufferings considered incurable
The treatment for the new disease cannot be considered until a complete picture of the old symptoms is obtained. Due to gradual progress of the chronic disease, many symptoms are produced one after another, and with which the patient might have been living since long.
During this course some serious diseases develops which are the result of the existing chronic disease. Patient ignoring of the old symptoms, thinking that they are incurable, seek treatment for the new disease. so the complete picture cannot be obtained. 

11. Un homoeopathic homoeopathic medicines
Some doctors usually prescribe complexes and tonics, eye drops and nasal drops to their patients. Each complexes/tonics contain 5_6 medicines. When they are administered, it will produce their own symptoms which will be more dangerous to the patient than natural disease.
So that, it would not have been possible for the homoeopathic medicine to overpower the natural disease and cure it. (usually homoeopathic medicines are more powerful than natural chronic  disease.
*Complexes and tonics are not prepared according to symptom similarity.
*They will produce their own symptoms (proving) and create a medicinal chronic diseases.
*This will mix up with the natural chronic disease and make a complex disease which will be incurable.

12. Self medication
If the patient get well by self medication, he does not come to a doctor. But if the symptoms remain, he come to the clinic. As a result of prolonged medication the symptom remain suppressed and cause a problem for the physician.

13. Mixed miasmatic disease
There are certain diseases which have a combination of psora, syphilis and sycosis in a complex ; it is very difficult to penetrate in these cases.

14. One sided disease 
These diseases present too few symptoms for a judicious prescription.

REFERENCES
Castro : Logic of Repertories
Ritu : Study of repertory
Dhawle : Principles & Practice of Homoeopathy