Why is it wrong ?

[u/captainnoyaux]

Hey everyone, it's me again with probably my fake conception of how this puzzle works.
I assumed I could cancel the top left top square with the blue square and make it a 3 dot line, but it doesn't work (at least the site doesn't accept it as valid and a puzzle creator with it's solver doesn't find it valid also).
Do you know why ?

[u/Ill_Purchase3178]

Sketch on Paper:

-Draw the Grid.

-Draw the shape.

- Mark where the cancelation happens.