Board Thread:General Discussion/@comment-26006155-20181229180615/@comment-26006155-20190127234237

Considering that The Silver Key is one of the ultimate secrets in Undertale, I doubt Sans was actually that careless with it.

In order to get that, you first have to get The Key To Sans' Room.

This item was placed on the keyring of one of the phones given to Frisk either by Toriel, or Alphys, in what has to be a very deliberate manner.

But Frisk the Amnesiac only realizes what this key is after discovering the special trick of talking to Sans, then rewinding time to talk to him again, and AGAIN.

Sans will only engage in this dialog with Frisk if and only if Frisk is 100% innocent at the time. Otherwise, Frisk will never learn about the key he already has.

This setup *has* to be a test.

Toriel, Sans, Papyrus, and Alphys knew Frisk was coming from the beginning, and put so many things in motion to test him, while also trying to guide him and protect him as much as possible without ruining that test.

And the goal? To find someone who could finally save monsterkind.

No, I don't think Sans was just thoughtless about where he put the key. This was one of the most deliberate decisions ever made by a time traveler.