driving force
nounUK /ˈdraɪ.vɪŋ fɔːs/
US /ˈdraɪ.vɪŋ fɔːrs/
The main thing that makes something happen or keeps it going.
Curiosity is the driving force behind most scientific discoveries.
OTHER MEANINGS
2. A person who leads and inspires a group or project.
She was the driving force behind the new community garden.
3. In physics, the force that propels a vehicle or machine forward.
The engine's driving force pushed the train up the steep hill.
4. An inner urge that pushes someone to act or succeed.
His driving force was the wish to help his family.