Proverb: 'a wise man changes his mind' — a saying meaning that a sensible person can and should change their stance when circumstances change.
上司は急に戦略を変えた。ある意味で『君子は豹変す』だ。
The boss suddenly changed strategy. In a way, 'a wise man changes his mind.'
歴史の教科書でこの諺（ことわざ）を見かけた：君子は豹変す。
I saw this proverb in a history textbook: 'a wise man changes his mind.'
Proverb (colloquial nuance): used to say that wise people will abruptly change behavior without hesitation; emphasizes adaptation and decisiveness.
政治家の突然の転向を見て、友人は『君子は豹変すだね』と呟いた。
Seeing the politician's sudden switch, my friend muttered, 'a wise man changes his mind.'
状況が悪化したので、リーダーは方針を一変させた。君子は豹変す、ということか。
Because the situation worsened, the leader completely changed policy. Perhaps 'a wise man changes his mind.'