The blossom end, and the sixteenth of an inch
Updated
What is actually there
The blossom end of a cucumber carries enzymes that break down pectin, which is the structure that makes a pickle crisp. They do not stop working because the cucumber went into brine. Left in place they keep working through the fermentation and into storage, which is why a batch can be firm when it is packed and soft when it is opened.
This is why trimming is specified rather than suggested, and why it appears on both problem tables rather than just one. It is not a quick-pickle technique or a fermenting technique. It is a cucumber fact.
Which end
The blossom end is the end away from the stem. If you are working from a crate where the stems have already been removed and you cannot tell, trim both ends. The yield cost is small and certain; the softening cost is large and probabilistic, which is the wrong trade to take.
Why it gets skipped
Because it is per-cucumber labor arriving in the one part of the year when nothing has slack. A picking window is short, the cucumbers are already in the building, and trimming is the step that feels optional because nothing visibly goes wrong when you skip it. Nothing visibly goes wrong for weeks.
Plan the labor rather than deciding about it on the day. If the volume makes hand-trimming impossible, that is a real constraint and it should change what you buy or how much you take at once, rather than being absorbed by dropping the step.
What it does not fix
Trimming does not compensate for a weak brine, a hot room or a long delay between field and jar. It removes one named cause. The others have their own pages and their own fixes, and a maker who trims religiously and ferments at 84F will still get soft pickles.