I am always amazed how few developers document their code.

I always hear:

"I write code that is easy to read" - Great but well written code can't... tell you why it was done this way, what it is actually supposed to do, how people should use it, how people shouldn't use it.

"I don't have time" - When is a developers time constrained by typing? Unless you type one word a minute you have time type create documentation.

Documentation is even helpful when creating the code. As ideas or thoughts change medium... from brain to paper or to sentence form. I see the problem differently, which gives them better understanding before wasting time creating something that isn't going to work.

Documentation is also helpful for two other people: Those who are not you and your slightly older self.