light a fire under someone
light a fire under (someone or something)
To motivate someone or something to take action. The deadline really lit a fire under us—we never would have gotten all that work done otherwise.
light a fire under someonemainly AMERICAN
If you light a fire under someone, you force them to act with more energy or to do something better. They need to improve their technical research and light a fire under their marketing team. It's hard to light a fire under people who don't think anything is wrong. Note: There is a story that some American farmers in the early part of the 20th century used to light fires under particularly stubborn mules that were refusing to move, in order to make them do so.