#1 Grammar Error

Would you like to know the #1 Grammar Error?

Hint: The word involved is small and it's contained in this sentence.

That's right: its vs. it's
Yet the two rules are actually quite easy to remember.

Rule 1: When you mean it is or it has, use an apostrophe.
Examples:

* It's a nice day.
* It's your right to refuse the invitation.
* It's been great getting to know you.

Rule 2: When you are using its as a possessive, don't use the apostrophe.
Examples:

* The cat hurt its paw.
* The furniture store celebrated its tenth anniversary.