How has the focus of marketing and sales shifted from funnels to flywheels?

According to Brian Halligan, businesses should move from traditional sales funnels to flywheel models. The key principle is applying force to your flywheel—the more force applied, the faster it spins. In the 1990s, the best ROI came from investing in the 'engage' stage through sales representatives who had information advantages over customers. By the mid-2000s, this shifted to the 'attract' stage as prospects gained equal access to information, requiring marketers to create compelling content. Today, the most effective investment is in customer delight, as satisfied customers drive word-of-mouth growth, making this stage the highest-return area for business growth.