The Patient's Side
The way health insurance works (or doesn't really), is that very few patients have long-term relationships with doctors because they have to keep changing them. Employed patients are mostly at the mercy of the employers and what coverage they provide. Self-employed, under-employed and unemployed patients might go years without a doctor's care. Once they get to the current health care provider, it is hard to catch him or her up in the short time allotted in regards to health history.
Often, patients have felt intimidated by a prior physician about being turned away with illnesses that are labeled "in their heads." Once they see a new physician, they often omit symptoms vital to diagnosis because of prior abrasive treatment.
The Physician's Side
Physicians generally fall into two categories: The under-prescribers and over-prescribers. Some have colored perceptions about experiences with prior patients who were "drug seekers" or labeled as such. This makes doctors weary about prescribing medications that have dependency dangers. The over-prescribers don't take time to get to the real issues and might feel pressured by patients who demand drugs they saw on TV.
Physicians often also don't understand why patients took so long to ask for help and wonder why they don't get health insurance. They might see holes in medical care and medical history as an indicator that the patient was not willing to get better, when the truth boils down to money (lack thereof).
The good physicians who don't go by extremes are often stifled by the rules of HMOs, PPOs, the fear of law suits, or simply a big workload.