1. John discovered the hard truth about responsibility. He didn’t get his college application in on time and the school won’t reconsider. It was a hard pill to swallow, but he had to learn the hard way.
2. Jill thought she was a good singer. When her brother told her she was tone-deaf, it was a bitter pill to swallow.

The expression suggests something that, like a pill, is unpleasant but cannot be avoided.