We are taught writing at a very young age. Hence writing becomes a subconscious process from very early stages in our life. It becomes a habitual activity like tying shoes or driving. We do not have to put any extra effort to perform the action of writing. While writing, we use the conscious as well as the subconscious mind. The conscious mind tells us what to write and the subconscious mind guides and tells us as to how to write. Hence, handwriting shows a distinct impression of the person’s mind and thought process.
The real driving force behind every habit/ action/ characteristic of a person is the thought itself, that is the subconscious thought. And all of this is reflected in the handwriting and signature. Every person has a different kind of mind (conscious and subconscious), mindset, thought making mechanism and thought process.
There will be common or similar traits in different handwritings. But every person has a unique set of traits and characteristics which makes each handwriting unique and distinguishable.