Pull the cake out early and it collapses in the middle. Looking done and being done are different.

The outside sets first, which is exactly what makes it a bad signal. Brown on top and raw underneath happens every time somebody trusts the surface, and the collapse arrives later, in public, when it gets cut into. Looking done is the earliest stage of being done, not the same stage.

Test the middle before you call something finished. Can you explain it without the notes, can you do it tired, does it hold up when somebody asks the second question. The surface is easy to fake and the structure is not.