Swallow a bitter pill

Eat humble pie / Eat crow


Mandar giù un boccone amaro

Masticare amaro / Inghiottire amaro


Meanings
Fig.: having to accept an unpleasant situation 

Examples
The famous rock band decided to split up and call it quits for good! The band's millions of fans have no choice but to swallow the bitter pill and accept the harsh reality
Il famoso gruppo rock ha deciso di sciogliersi e di dire basta per sempre. Ai milioni di fans del gruppo non resta che inghiottire l'amaro boccone e accettare la dura realtà

The great athlete thought he could easily win, but when a rookie beat him by the smallest margin, he swallowed the bitter pill and ran off to the locker room
Il fortissimo atleta pensava di poter vincere facilmente, ma quando un novellino lo ha battuto, seppur di un soffio, ha masticato amaro ed è subito andato negli spogliatoi

Paul was absolutely sure that his promotion was in the bag, but he had to swallow a bitter pill when he learned that Louis, his younger and, in his opinion, less experienced colleague, was chosen instead
Paolo era convinto di avere la promozione in tasca, ma ha dovuto inghiottire amaro quando è stato scelto Luigi, il suo collega più giovane e, secondo lui, meno esperto

Origin
A medicine could be bitter and bad tasting, but you have to swallow it anyway and accept it