The examined concept is the precise surgical definition of $TME$ for rectal carcinoma.
The rectum is wrapped in the mesorectum - a parcel of fat, lymph nodes and vessels enclosed by the visceral mesorectal fascia. Rectal cancer spreads into this parcel, so curing it requires removing the parcel whole, with its covering fascia uninjured (an intact circumferential resection margin).
Heald's principle is to develop the bloodless areolar plane (the "holy plane") between the mesorectal fascia and the presacral fascia, and to do so with scissors / diathermy under direct vision - i.e. sharp dissection - lifting out the rectum and its mesorectum en bloc as one specimen.
Why the rest fail:
$\bullet$ Removing only peritumoral fat to leaves nodal deposits to recurrence.
$\bullet$ Blunt finger dissection to ruptures the fascial envelope, spills tumour, injures autonomic nerves.
$\bullet$ Internal iliac ligation to irrelevant to mesorectal clearance.
\[\boxed{\text{TME} = \text{sharp en-bloc excision of the entire mesorectum as one unit}}\]