Every piece of writing, from fiction novels to web content, has a voice. A professional writer will be able to recognize and manipulate this voice to suit a purpose. That purpose varies widely depending on the application of the writing required.
For instance, a fiction novel may use an epic voice to tell a story about adventure or tragedy, something that harkens to the days of long ago and kindles the flame of passion and danger in the reader. A poem may use an angry voice to incite the reader, or a voice of sadness to make them share the writer’s sorrow. A non-fiction paper, such as a thesis, will use an educated voice to lend authority to the words.
It’s often natural for a writer in those mediums to find the correct voice. We read a lot of those types of works, and we will naturally tend to a similar voice when trying our own hand at it. Many very successful writers are noteworthy for *breaking* these tendencies. A new type of voice for an old genre can make it unique and interesting.
What is more difficult to work with, is the voice of content writing and advertising.