meaning of "take the law into your own hands"

Business English Lesson, Advanced Level

ESL/EFL Test #51 [color=blue]“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
© mind
(d) control

Business English Lesson, Advanced Level

ESL/EFL Test #51 [color=blue]“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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Attempt to act as police, judge and jury.
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