What does `Some courtesy is needed` mean in Level 4?

It means you should tap the closed right-hand door to knock before entering.

Why will the right door not let Boxy inside?

The door remains closed until it receives the direct courtesy interaction.

Wait for the purple doorway to open, then move Boxy through it.

Brain Riddle: Tricky Box level guide

easy

Courtesy opens the closed right-hand exit: walk Boxy across the ground, tap the door itself to knock, and enter only after it swings open.

If the player asks you to sign in, open the video on YouTube instead.

Assuming the level is solved by repeatedly walking into the closed door.
Using the jump control against the door instead of interacting with the door object.
Moving away without checking whether the knock changed the doorway state.

Board notes 5 details

Layout: A left arrival door and a closed right exit door stand on the same flat ground, with Boxy emerging at the left and the courtesy prompt centered above them.
Goal: Open the right-hand pink door through a direct courtesy interaction, then move Boxy through it.
Opening: Walk right from the left door and stop directly in front of the closed exit.
Danger Zone: Jumping against the right door or repeatedly walking into it leaves it closed because movement is not the requested courtesy action.
Mechanics: Tapping the closed exit acts as a knock and visibly changes it into an open purple doorway.

What does `Some courtesy is needed` mean in Level 4?
It means you should tap the closed right-hand door to knock before entering.
Why will the right door not let Boxy inside?
The door remains closed until it receives the direct courtesy interaction.
How do I finish after knocking?
Wait for the purple doorway to open, then move Boxy through it.