This proverb has been in use since at least the mid 16th century. In 1545 William Turner used a version of it in his papist satire The Rescuing of Romish Fox:
“Byrdes of on kynde and color flok and flye allwayes together.”
Quentin Tarantino realized he needed to leave his flock as a young adult. He was working in a video store (remember those?) and enjoying the benefits of watching movies, which were his passion. His co-workers were also making minimum wage, but he knew he was the smartest one among them. This made him feel comfortable – for three years – where he admits he “lost all ambition.” And then he woke up. He didn’t want to be an elderly man working in a video store, talking about movies. He wanted to MAKE them. So he had to leave his flock.
And he did.