The phrase has medieval roots, originating from knights accepting a duel by picking up a dropped gauntlet. When the senior manager dared someone to improve sales, I took up the gauntlet.
Pro Tip 2/3
Not Literal
It's a metaphorical expression and doesn't involve physical fighting in modern use. Despite the difficulty, she took up the gauntlet to complete the marathon.
Pro Tip 3/3
Demonstrates Courage
Using the phrase can imply that someone has the courage to face difficult tasks. He took up the gauntlet to defend his team's project.