On The Tonight Show, Josh Hartnett revealed Matt Damon gave him unhelpful advice against gaining weight for "Oppenheimer".

Josh Hartnett shared on The Tonight Show that Matt Damon gave him "unhelpful" advice during the filming of "Oppenheimer". Damon advised Hartnett not to gain weight for his role as a nuclear physicist, despite Hartnett already having gained around 30 pounds. Damon's general rule for roles is to not gain weight over 40 due to his own negative experiences with weight gain for past roles.