I get this question a lot. "Why do you write? It must take a lot of time..." I also get it's lesser cousin, the ambiguously worded half question "I started writing a book once" which is actually code for "is there a way you can help convince me to finish it?"
The answer to that second question is no. I cannot convince you to write anything, and this gets to the core of the situation. Writing is about need.
You cannot want to write a book like you might want some chocolate.
You have to need it, the way we need water and air and love.
If you are a writer, then you need to write as a way to think. Some people think through dance, some people think through spreadsheets. Everyone is different. Writers think by writing. It is a need, fundamental and pure, that cannot be put aside for when it is convenient.
If you want to write, you must tap into that need. What story do you have that needs to be told? What story is fermenting inside of you at this very moment? What thought has gotten trapped beneath your skin and begun to fester? Lance the boil - relieve the pressure - start writing.
Do not write a book because you think it might be neat, or because you think it's something fun. Do not write a story as something to add to your resume. Do not write your story to impress someone. Your story, if you begin it, is a living, breathing entity, and you cannot let it go out into the world half-formed. You must want it, not the end it will bring you.
Write because you will lose your sanity if you do not. Write because there is something inside of you that needs to be unleashed, something that if kept trapped and contained inside you will eventually shatter your soul.
Writing can be pleasant - writing can be fun. But in its truest form, it is the most uniquely human form of self-expression that we have. Do not take it lightly.
Write because you are human and you have a story that must be told. Tell it not because you'd like to, not because you'd enjoy it, but because you believe in it with every fiber of your being.
That's why I write.