There are many achievements in Lost in Random, and some of them can easily be missed. One of these is the Knock Knock achievement, which is a missable achievement that is only obtainable early in the game.
This achievement can be unlocked once Even wakes up after dreaming of Odd and the ghost. If you do not get Knock Knock before proceeding too far into Onecroft, the achievement will no longer be obtainable.
Related: How to get coins in Lost in Random
Once Even wakes, follow the ghost and leave your home. Speak to Astrid and convince her to let you pass. Continue and you will spot Lucky, Bernard, and Algot. From there you will have two paths to take. Take the left path and head down the tunnel. You will recognize this as the path you took to hide from Nanny Fortuna. This leads you back to your home.
Follow the path up to your door and interact with it. The narrator will tell you that Even should not knock. Keep interacting with the door and ignore the narrator who insists that you do not knock. After five attempts, the narrator will finally let you knock. Once you do so, you will receive the Knock Knock achievement. Make sure to get this achievement because you will not be able to later.