The reason DiNero repeats his lines a lot is because he can’t remember what comes next. It became his “style”, PLUS, when you’re Robert DiNero you can pretty much write your own lines.
Sharon Stone is another one who can’t remember lines. So she just flashes the camera while trying to think of what to say next. They all have their own little tricks. I’m only half kidding.
Brando had cue cards distributed all over the set when he was filming. He was terrible at learning lines.
I was actually stunned to hear de Niro stammer and appear nearly senile in interviews. I expected him to be sharp and clear spoken.