meaning of "take the law into your own hands"

[Thunu]

Business English Lesson, Advanced Level

ESL/EFL Test #51 "Legal Expressions", question 2

However angry you may get at what someone has done to you, the police always advise you not to take the law into your own ..........

(a) fingers
(b) hands
(c) mind
(d) control

Business English Lesson, Advanced Level

ESL/EFL Test #51 "Legal Expressions", answer 2

However angry you may get at what someone has done to you, the police always advise you not to take the law into your own hands.

Correct answer: (b) hands
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Can you explain the meaning of "take the law into your own hands", please?

Thank you
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Reach an agreement as ploughing, don't let argument happen at crops.

[Mister Micawber]

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Attempt to act as police, judge and jury.
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Native English teacher at Mister Micawber's