Hexagram 4, Méng (Youthful Folly): Line 6 (top)
蒙卦上九 · 山水蒙 · 中文版
上九：击蒙；不利为寇，利御寇。
The line (Legge)
In the topmost NINE, undivided, we see one smiting the ignorant (youth). But no advantage will come from doing him an injury. Advantage would come from warding off injury from him.
Small Image commentary
'Advantage will come from warding off injury:' - (the subject of this line) above and (the ignorant) below, all do and are done to in accordance with their nature.
象曰：利御寇，上下顺也。
In plain words
Striking at ignorance; it is not favourable to act like a robber, but favourable to ward robbers off. The top line is strong at the peak of the hexagram, and its teaching is severe; but severity should only keep harmful things out and must not turn into harm to the student. The Small Image says that warding off robbers lets those above and below go along together.
Applying it to your situation
If you need to correct someone sternly, this line suggests telling apart preventing mistakes and hurting people. Is your severity protecting the other person, or letting off your own feelings?
Position
A solid (yang) line in the top place, which is a yin (even) place, so it is not in its proper place. Its partner is line 3; one is yin and the other yang, so they respond to each other.
If this line moves
With this line moving alone, Méng changes into Hexagram 7 Shī (The Army). The Jiaoshi Yilin verse for this change (Chinese): 焦氏易林·蒙之师.
The hexagram
Hexagram 4 Méng (Youthful Folly). The Judgment: Meng (indicates that in the case which it presupposes) there will be progress and success. I do not (go and) seek the youthful and inexperienced, but he comes and seeks me. When he shows (the sincerity that marks) the first recourse to divination, I instruct him. If he apply a second and third time, that is troublesome; and I do not instruct the troublesome. There will be advantage in being firm and correct.
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English text: James Legge, The Yi King (Sacred Books of the East, vol. 16, 1882), public domain, as transcribed by the Chinese Text Project. Chinese: the received text. Offered for study and reflection, not as prediction. Plain-English readings and position notes by this site.