Why is it important for an author to focus on how their character speaks?

Details about a character’s relationships always come across in dialogue.
A character should always reflect the author’s speech patterns.
Dialogue is the only way to make sure a character is not one-dimensional.
Much of one’s personality comes across in speech.

There are a few reasons why it is important for an author to focus on how their character speaks. Firstly, much of one's personality comes across in speech, so the way a character speaks can help to develop their character and make them feel more real to the reader. Additionally, details about a character's relationships always come across in dialogue, so the way a character speaks can reveal a lot about their feelings towards other characters. Dialogue is also an important tool for avoiding one-dimensional characters, as it allows for the exploration of different sides to a character's personality. Finally, while a character may not always reflect the author's speech patterns, an author can use speech patterns to differentiate between characters and make them feel more distinct.