Scenario :
You had added a "friend" in Facebook ... but somehow after the Friend Request was sent, you realized that you shouldn't have sent it ... for one reason or another, you want to take it back but you don't know how to
You searched in vain on how to cancel it ... but couldn't find how...
... It's because it cannot be done in one step! ... Yup, you read it right ... It can be done, but not in one step ...
Here's How :
1) Go to "Settings" -> "Privacy Settings"
2) Type the name of the person in the "Block" box, then click "Block"
3) This automatically cancels the "Friend Request"
4) After this, the person's name will appear with an option to "Unblock" it.
5) You have the option to "Unblock" it, just in case you want to add that person again in the Future.