Might I shed some light into this matter? It is true that Celestia and Luna were the ones to find the Elements, but have we forgotten that Equestria was founded before their battle against Discord? Who is to say that the Tree of Harmony wasn’t discovered or created within that time period?
 
Celestia and Luna knew that it was called the Tree of Harmony. Maybe it is something that they were taught about when they were young, but they never knew everything about it? Maybe the Tree of Harmony was created by Star Swirl the Bearded or Clover the Clever? Maybe it is through their journals that the Alicorn sisters discovered the tree’s location? There is still that air of possibility and therefore a chance that a book about the Tree of Harmony exists.

@FanOfMostEverything  
The original analogy assumed you wanted to open the other person’s door.

@Mayojar77  
We appear to have gotten the analogy confused. Each of us is using his own door as the Lockbox of Harmony.  
…actually, I think at this point, it’s best to agree to disagree. It seems like neither of us is going to convince the other. Besides, does it really matter?

@FanOfMostEverything  
But if say you wanted to open my door, then the knowledge of where to get keys would be useless until you already had my key. You understand what I’m saying here?

@Mayojar77  
But I don’t care about your door beyond its similarity to mine. And once I know how you got keys for yours, I can get them for mine.

@FanOfMostEverything  
That won’t work. You would need a way to know what the key you need to open my door looks like in order to get another copy. If you do not have the exact key to open the door, or at least an identical replica, then you can’t get through the door.

@Mayojar77  
But knowing how you got them tells me where to get a new set for myself.

@FanOfMostEverything  
Not really.  
It’s two completely different things. Neither has the same circumstances and the outcome will likely be different. After all, the keys to your house won’t open mine.

@Mayojar77  
But at least it’s a starting point.

@FanOfMostEverything  
There is no reason something vaguely like this hasn’t happened, but as I’ve said, this has never occurred before. what works in one situation doesn’t always work in a similar one.

@Mayojar77  
This hasn’t. Something very much like it could have. And the only way to be sure, as far as Twilight is concerned, is to look.

@FanOfMostEverything  
This has never happened before. Like, actually never. There would be no information regarding it.

@Mayojar77  
SunnySide’s argument is that while no one has ever seen the Lockbox of Harmony before, there may be analogous examples of mysterious locked magic boxes in history. From those examples, Twilight would at least have somewhere to begin with her new MacGuffin.

@Mayojar77  
Mature.

@SunnySide  
I’m sorry, This user can’t respond to your comment due to high concentrations of Condescending-bitchium, one of the most highly toxic radioactive elements in existence. Please quarantine yourself from the internet and undergo treatments to remove the traces of said element from your system.

@Mayojar77  
Okay, I didn’t say specifically information on the elements can be found in a book.  
Quit being dumb and think for once in your life.

@SunnySide  
You’re not getting what I’m saying.  
What I’m saying is that there’s literally no way that information could be found in a book. None.  
The only character with any real understanding of how the elements work was evil until recently, and thus wouldn’t have written a book about it, and even then, only one actually trusts him to tell the truth in any measure.

@Mayojar77  
You don’t… You don’t fucking get it  
You aren’t getting what I’m saying.

@Spiritus Arcane  
Celestia isn’t omniscient, you know.

@SunnySide  
The thing is, nobody but Discord knew about the Elements until Celestia found the Elements, And going by his reaction, they had never even been used before.

@Mayojar77
 
@Japanese Teeth  
Pretty much this.  
You CAN predict solutions to problems even without evidence via assumptions and patterns that could very well have happened before in different circumstances. All it takes is knowledge of what happened that was similar, and that could give someone a solution to a problem; In example, the box.  
Considering we don’t really have any information other than “Shit dudes, This is a fuckin’ box, We should open dat. It’s important lookin’” and that the princesses MIGHT have something in the diary.  
Hell, For all we know, she doesn’t find anything in the diary or any of the books, and needs some more discovery or knowledge that we don’t even know of yet.

@Mayojar77  
The chest itself might not have happened before, but there might be books about similar magical phenomena that might shed light on this particular occurance.

Hey Celestia wants to do the whole ‘Mysterious Mentor’ bit AGAIN instead of just telling her what book to look for? Get’s her diary read by the Mane 6.

i’ve always wanted to write like a sleep deprived baboon