The Voice (Ju Men, 巨门) in the Self palace (Ming Gong, 命宫)

What the classic says, Zi Wei Dou Shu Quan Shu (紫微斗数全书), volume two

Darkness, its transformed nature (化暗), and the star of dispute. At Rat (子) or Horse (午) it sits well, and with the Merit transformation (化科), the Power transformation (化权) or the Fortune transformation (化禄) in trine, high office. With the Blade (擎羊) in the seat of the self, or the Flare and the Ember (火铃) met, things run crooked: quick-tempered, upside-down, a hundred matters and no order among them. Well placed in a woman's chart with the two Aides (左右) added, honour and long life.

巨门水，北斗化暗，主是非。巨门入男命吉凶诀：巨门子午二宫逢，局中得遇以为荣，三合化吉科权禄，官高极品衣紫袍。巨门守命遇擎羊，火铃逢之事不祥，为人性急多颠倒，百事茫茫乱主张。巨门入女命吉凶诀：巨门旺地多生吉，左右加临寿更长，女人得此诚为贵，帘卷珍珠坐绣房。相貌清奇多近宠，不然寿夭或凶亡。巨门入限吉凶诀：巨门主限化权星，最喜求谋万事成，虽有官灾并口舌，逢凶化吉得安宁。巨门入限动人愁，若遇丧门事不周，士庶逢之多惹讼，居官失职有丁忧。巨门限陷最乖张，无事官非闹一场，哭泣丧祸终不免，破财呕气受凄凉。

Part of this clause fixes a woman’s outcome by her sex; it is left out here, in the Chinese as well as the English, as everywhere on this site.

“Well placed” and “badly placed” refer to the star’s brightness in the branch the palace falls on: the same star in the same palace reads differently bright and dim, and the clause says how.

Source

And in the chapter of questions on the stars (Zhu Xing Wen Da Lun, 諸星問答論)

a lifetime of disputes — things said, and things said back

在身命一生招口舌之非

How this placement actually turns up

• Well placed (exalted or strong) in 68% of those charts, badly placed (fallen) in 17%, in between the rest.
• Alone in the palace in 51%; sharing it with The Strategist (天机) 17%, The Sun (太阳) 16%, The Blessing (天同) 15%.
• Carries a birth-year transformation in 32%: Fortune (化禄) 11%, Power (化权) 10%, Trouble (化忌) 10%.
• How often the conditions the classic’s line names actually occur — one of the four difficult stars (擎羊陀罗火星铃星) in the palace with it: 30%; one of the six helper stars (左辅右弼文昌文曲天魁天钺) with it: 40%; Lu Cun (禄存) with it: 9%.

Counted by casting every day from 1950 to 2009 at each of the twelve hours — 262,980 charts, 8.3% of which have The Voice here (every main star sits in every palace in about one chart in twelve). A count, not a reading.