https://dune.fandom.com/wiki/Gom_Jabbar

The Bene Gesserit also made extensive use of the Gom Jabbar, especially when they tested the humanity of certain individuals. In such circumstances, the device was placed against the subject's neck and acted as a deterrent for them backing out of the test. Such a method was used by Reverend Mother Gaius Helen Mohiam against Paul Atreides before his arrival on Arrakis.

The gom jabbar test would be to determine whether an individual's awareness was stronger than their instincts. If their awareness of the gom jabbar's presence was strong enough, it would override their instincts to withdraw from the test, which usually involved great physical pain.

Saw this dramatized at around age 10 in David Lynch's version of Dune. It's always been a persistent notion about my personal model of adulthood as a human.

It's a belief of mine that a good human should be able to consistently intercede with discipline on pain & fear to do what they thoughtfully intend. Not that I've done spectacularly at achieving it, but it's an ideal.

Seems a hard thing to maintain, seeing as we're all mech pilots in meat suits and the meat suits are hard to override consistently. But, it's a good fight to keep up.