"I think the highest turnover job of any Silicon Valley executive position might be the CMO." Airbnb's @bchesky says he has a huge amount of respect for people in marketing because it's one of the hardest functions in a business. "Because once something works, it almost becomes stale. Because everyone does it." "Part of my theory is that what works in marketing changes every few years and you have to be adaptable. Your old playbook gets outdated." "It's this thing called 'banner blindness.'…