https://www.metv.com/stories/james-arness-quit-gunsmoke-just-before-the-series-started-filming-this-was-the-phone-call-that-convinced-him-to-return

One fateful call changed the actor's life.

This Gunsmoke producer said that the cast's loyalty to one another was what made the show so successful (https://www.metv.com/stories/this-gunsmoke-producer-said-that-that-casts-loyalty-to-one-another-was-what-made-the-show-so-successful)

The secret to success? Friendship.