It's harder than ever for companies to get their marketing messages in front of the right customers. One increasingly popular -- but also risky -- tactic is fastvertising, the rapid development of ads that tap into a cultural moment, aiming to increase brand relevance and awareness. Harvard Business School associate professor Ayelet Israeli shares pitch-perfect examples, including those from her coauthor, the actor Ryan Reynolds, and his marketing firm Maximum Effort. She explains the importance of timing, describes the talent, culture, and processes you need to succeed, and outlines how to extend the impact of these ads. Ayelet, along with Leonard Schlesinger, Matt Higgins, and Ryan Reynolds, wrote the HBR article "Marketing at the Speed of Culture."