"Usually it's because of the people," Variety quoted the actor as answering.
"And when armed with material that's compelling you have to ask yourself -- does this help? Does this need to be in the world?" 'The Post' actor added.
Meanwhile, Phoenix who shared the award with 'The Post' actor, shared his source of inspiration apart from thanking others in his Tribute award acceptance speech.
"My mother is a constant source of inspiration, and everything I do, I do for her," he said.
His upcoming release 'Joker' was recently premiered at the festival and also won the Golden Lion award at the Venice Film Festival.
Streep, on the work front, is awaiting the release of 'The Laundromat' on September 27 which first debuted at the Venice Film Festival.