There are different acting techniques out there, but if you’re going to make people really feel who you’re playing, you have to, at the very least, understand the motivations of a character and why they do the things they do. For Modine playing Brenner, that wasn’t a pleasant experience:
“Your body doesn’t know it’s acting. Even though I’m memorizing lines and I understand the physical aspects of acting, you put your body through whatever that character is going through. It can be very destructive to your body. I don’t ever want to get in the skin of someone like Dr. Brenner again.”
Modine appeared in seasons 1 and 4 of “Stranger Things,” and his final appearance (maybe?) made it clear that he really internalized Brenner’s feelings. There is such a desperation in his final moments for Eleven (Millie Bobby Brown) to understand him. There is a sense that while he knew other people wouldn’t understand his choices, he really did believe it was all for the best. Of course, it’s hard to justify when that thing you believe has destroyed the lives of children and is crushing an entire town, threatening it with destruction.