Throw in the towel
Definition 1 of 1
Pro Tip 1/3Sports Origin
The phrase originates from boxing, where a trainer throws a towel into the ring to stop the fight. 
He was unable to match his competitor's skills, so his coach decided to throw in the towel.
Pro Tip 2/3Metaphorical Use
Used metaphorically to express giving up on challenges beyond sports, like work or relationships. 
After years of trying to make the relationship work, she finally threw in the towel.
Pro Tip 3/3Not Literal
The phrase is never used in a literal sense in modern English; it always indicates quitting an activity or effort. 
When the software development became too taxing, the team threw in the towel.