David, a 20 year old who thinks too much

"I can't believe it..." David looked at the inconspicuous with wide eyes. It looked like it could pass as a somewhat thick science book if someone put the right cover on it and yet it held this much power.

He flipped to the next page and wrote "The rulebook" across the top. He couldn't treat this lightly and couldn't let this get into anyone else's hands. The only person He could fully trust is himself.

[New Rule: The person writing this rule will be recognized as the owner of the rulebook from this point onwards.]

[New Rule: Only the owner of the rulebook will be able to perceive and write in the rulebook.]

[New Rule: The owner of the rulebook will not be disturbed when writing in the rulebook and the people around the owner will think nothing of the owner writing in a book that they cannot perceive.]

David spent 10 minutes deciding the wording and content of the rules. The new rules felt like they would take care of keeping the book as his. As he looked at his work, he thought about how he would keep a book this size on him at all times.

[New Rule: The rulebook will teleport to the owners hands with a pencil and eraser when the owner wishes to write in it.]

[New Rule: The rulebook will go to a designated storage location when not in use.]

[New Rule: The rulebook is indestructible.]

As he wrote these rules, he began feeling more excited. With each rule written on the page making him feel more anticipation for the future possibilities.

David took a little bit of time to calm himself down and ordered a cup of hot chocolate. He couldn't get lost in what this book had to offer. He sat in thought while waiting for his order to arrive, there was so much that he didn't know about this book. He pondered on what ways he could test the book and what the limits could be as he got his cup. Ultimately, he could only ask the book to tell him because there was no other way to test this for now.

[New Rule: A note will appear in front of the owner after this rule is done being written. It will state if the rules have any costs that will affect the owner and the limits of the rulebook.]

A small square note had appeared in front of David.

"There is no cost of using the rulebook that will affect you and there are no limits that would get in the way of your desires."

Reading this scared David. It sounded too natural, it also knew him well enough to assume his "desires". He didn't like how alive it seemed now. He was taking this too lightly. The world seemed to grow silent around him as he thought about whether he should use this book or not. A book that could grant all of his wishes lied in front of him, but could he safely rely on it? He tried express his will to not write anymore and tell it to go to the desk in his room. The rulebook faded away as if it was never there, leaving the pencil that rested on it to fall.

He paid and decided to walk home, he could use the time to think. It had started raining around when he wrote his fourth rule, but he still wanted to walk. He got home 30 minutes later and headed straight for his room. The book lied there on his desk, just as he had imagined it in the coffee shop, he sat in his desk chair an stared at it. After taking some breaths, he opened it and started writing once again.

[New Rule: If a question is written in this rulebook, it will be answered in a language that the owner understands. The answer will appear under the question and will be written in the colour blue.]

[Is the rulebook considered alive and is it capable of thinking]

[The rulebook is not "alive", but it can think.]

[Why does the rulebook exist and why would it let me write the rules?]

[The rulebook simply exists, the concept of rules is everywhere and everything is built upon them. Sometimes having someone create new ones and throw the balance into chaos is fun, so the rulebook is granted to a sentient being until everything resets once again. Stop thinking so much and have some fun.]

It seemed like the only point of the rulebook was to give some fun to whoever was answering. This answer had made David much less scared of the rule book for some reason. It just made sense to him that something that could make the rulebook would probably be bored and do something like this. While David was lost in thought, a random page had split open before the words "Rule: David will use the rulebook to satisfy his desires" appeared. The page had then healed, concealing the rule.