中国人常说“一诺千金”，意思是“A promise is weightier than one thousand bars of gold”。做出承诺就应该去兑现，不应该“出尔反尔”。
“出尔反尔”，汉语成语，多指自己说了或做了，后来又反悔。比喻言行自相矛盾，反复无常，说话不算数（promise and then deny in succession;be inconsistent in one's words）。可以翻译为“go back on one's word”或“ renege on one's word”，表示“to break a promise that one has made；to not do something one said one would do”。
You made a commitment to support our project, and now you've gone back on your word!
I am mad at you because you reneged on your promise!
I hate to go back on my word, but I won't pay you $100.