We were all taught to write in a specific way at school, when we were children at but it is evident that no one continues to write exactly the way they were taught and everyone's handwriting looks different. In fact as soon as someone can write, he or she gradually alters the shape and sizeof letters in accordance with one's likes and dislikes.
The reason is that our personalities affect the way our handwriting develops after we were taught to write. This is because handwriting is the pattern of our psychology expressed in symbols on the page and these symbols are as unique as our own DNA.
When you get to know a person's handwriting well, you can recognise whose script it is, just as if it were a well-known painting or a photograph. Graphology is based on the principle that each individual's handwriting has a character of its own and this is entirely due to the uniqueness of the writer's personality.
So it is the writer's deviation from the copybook learnt that allows expert graphologists to assess, accurately the character and capabilities of the writer.
In fact graphologists are exceptionally fortunate as that they see before them, in black and white, the pattern in symbolic form of a writer's whole psychological profile. By contrast, psychoanalysts and psychotherapists all over the world must formulate their opinions solely on the basis of what is told to them over a period of time by the client in question.