There's no such thing. Isn't that funny? Seriously, we all live in our own realities and we think they are true, and you know what? They are . . . for each individual.
In a court of law, a witness on the stand promises to tell the truth, the whole truth and nothing but the truth, but what happens is that person tells the truth according to them. It's not wrong. It's just reality. =)
For writers, this is a wonderful thing to play with. Our job is to draw people into our reality, cause them to laugh, cry and root for our hero. Great writers do this with ease.
The only advice I have is to be sure to make your reality an exciting place to be. There's nothing more boring than a boring reality, but then, that's just me.