The expression a bitter pill (to swallow) means something very unpleasant that must be accepted.

For example:

Losing to a younger player was a bitter pill to swallow.

This defeat was the most bitter pill to swallow.

The knowledge that his friends no longer trusted him was a bitter pill to swallow.

Failing the bar exam was a bitter pill to swallow, but he plans to try again next year.

Getting a poor performance review was a bitter pill to swallow, but it made me a better worker.

It was a bitter pill for her brother to swallow when she married his enemy.

Tradução: um fato difícil de engolir, um remédio amargo, algo difícil de aceitar ou digerir.