Please explain. Why does the mesh get so messed up Trim - Plane vs Qube

See the Video.
Please explain for beginners. Is it possible to trim a Plane clean ?

When using Trim on a plane, you have to turn off the “fill holes” option. It makes the cut and sees that there’s only one side, so it thinks that the entire edge of the plane is a hole to close.

:slightly_smiling_face: Thank you - now it is quite Logical…