You make an appointment with your doctor.
You're looking for a solution to your medical issue.
You want the doctor to correctly diagnose what problem you have.
You want him to recognize your medical condition.
After you tell him about your problem, he's going to ask you questions.
"How long have you had this?"
"When did you notice this?"
"What did it look like at first?"
He's digging for information.
Information only you will know.
He'll then ask you about your past.
"Have you ever had this before?"
"Has anyone in your family had this before?"
"Have you tried this medication?"
"What type of reaction did you have?"
Your doctor isn't just making polite conversation.
The only way he can accurately assess the problem is to get as much information as possible.
Where? When? How? Who? Why? What?
He's not asking you these questions just for the hell of it.
He has to rule in or rule out different medical conditions based on your complaints, your medical history, findings on physical examination and more.
Admittedly, not everyone has an excellent memory and may leave out certain salient points.
If you bring a lawsuit claiming that your treating doctor failed to diagnose or treat you appropriately and now you suffered significant injury because of that, the defense will look through and scour your medical records to make sure you were totally honest and upfront with the doctor during your treatment with him.
If by some chance you left out certain information that would help the doctor evaluate you and treat you, they will point out that your failure to include critical information in your medical history led the doctor to certain conclusions that he would not have otherwise come to had you provided the correct information.
They will compare it to the information you provided to the doctor you are suing.
If there are discrepancies, they will use that against you to show that you failed to provide sufficient information to the doctor in order for him to make an educated decision about what course of treatment to offer to you.