David Harbour plays police chief Jim Hopper in “Stranger Things.”

Harbour revealed that he suffered panic attacks on the “Stranger Things” season one set.

He said he thought the show would flop.

Harbour also said Netflix did not advertise “Stranger Things” in its first season.

Harbour said watching the series achieve success was satisfying.

Harbour called the “Stranger Things” script “terrific” when he read it.

He didn’t know it would blow up.

Harbour said he is proud of his co-stars Millie Bobby Brown and Finn Wolfhard.

He shared his worry for them having so much fame at such a young age.