Get something into one’s head
(1) = to begin to think that something is true even though there is no good reason for believing it.
(2) = suddenly decided to do something in a way that seems foolish or surprising.
(1) Mary somehow got it into her head that she needed to come from a prestige family in order to get into Harvard University .
(2) She somehow got it into her head to become a nun and cancelled her wedding.
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P.S. My Chinese translation is not good. If you have better translation, please let me know. Thanks!