Lose heart
Definition 1 of 1
Pro Tip 1/3Emotional Tone
The phrase carries an emotional weight, often used to express empathy with someone's disappointment. 
I know you're close to giving up, but don't lose heart—things will get better.
Pro Tip 2/3Motivational Context
Commonly used to encourage others to continue trying despite difficulties or setbacks. 
The team was behind, but the coach told them to never lose heart.
Pro Tip 3/3Not Literal
The phrase is not about actually losing a part of the body. It's a metaphor for losing courage or hope. 
He was about to lose heart, but then he remembered his family's support.