Freud theorized that psychological symptoms were the product of repressed memories.
Once this memory was found, released and 'let go,' then the patient could be cured.
Jean Martin Charcot was one of Freud's mentors.
He it was who first formalized this idea.
Charcot was a neurologist, not a psychologist, and he made studies of the workings of the brain long before more sophisticated equipment made its appearance.
Tools such as X-ray machines, EEG and recording equipment that could actually image what was happening to the brain.
Unfortunately, then, in Charcot's time, disorders such as epilepsy and Tourette's Syndrome were sadly mis-diagnosed.
Tourette's Syndrome is an inherited neuropyschiatric disorder which becomes apparent in childhood.
It manifests itself by multiple physical 'tics' and sometimes verbal sounds, too.
They're not always apparent, for they come and go.
As with hysteria, he diagnosed them as psychological disorders, which they are emphatically not.
In Charcot's and the young Freud's time, even concussion wasn't understood.
An example of this was that of a workman delivering flowers for a florist to an address in Paris.
He finished unloading and turned his barrow for the journey home.
He was holding the handles of his barrow tightly, when he was hit amidships by a speeding carriage.
The poor chap was spun through the air and landed with a terrible impact on the ground.
When they picked him up, although he was unconscious, he didn't appear to have any other injury.
He spent six months in hospital.
It turned out that he was partially paralyzed, suffered severe nose-bleeds, had a permanent headache, suffered seizures and reported 'blanks' in his memory.
Charcot completely failed to recognize the symptoms of concussion, or closed head injury, and since the poor man couldn't recall the accident at all, Charcot concluded that the memories must have been so terrible that he repressed them.
The seizures he put down to hysteria.
Now, certainly no modern neurological specialist would put put this man's symptoms down to anything psychological.
However, this gives you some idea of how this repressed memory idea took hold and indeed many other psychological ideas which sprang from the minds of Freud and Charcot mis-informed and influenced psychologists - and indeed the general public - for generations to come.
When you think about it, this whole theory of repression could well have come from this one incident of the poor florist.
The truth is that if something terrible happens to us, we usually remember it, although we may choose not to think about it.