Why does Elena Verna say a growth model needs replacing roughly every 18 months?

Elena Verna, who has run growth at Amplitude, Miro, Dropbox and SurveyMonkey, thinks in loops rather than funnels: a funnel is linear and spends itself, while a loop feeds its own next turn, which is what makes growth sustainable, predictable and hard for a competitor to copy. Her point about shelf life follows from that. Whatever loop is working today saturates, so she says a growth model needs updating roughly every 18 months, and teams that treat theirs as permanent quietly stop growing. She is equally specific about what does not work: hiring growth specialists before roughly a million dollars in ARR, because you cannot outsource getting your initial traction; using a growth team to rescue a declining business; expecting a redesign to lift performance, since redesigns are always a step back first; and leaning on paid channels, because renting access through Google, Meta or TikTok is neither scalable, sustainable nor predictable. Her Dropbox example makes it concrete: today's growth runs on file sharing and marketing loops, not the famous referral program, which never transferred to B2B.