"A low payback implies profitability will come sooner rather than later (and you can sustain high growth rates)." cloudedjudgement.substack.com/p/what-it-take… 
"You calculate the Rule of 40 by combining the growth rate and the operating margin (YoY growth + operating margin). Here I’m using GAAP operating margin."
"Growth comes at a cost, and by adding operating margin (which is generally negative) to the high growth rates in SaaS we get a better understanding of what that cost is and how sustainable / profitable that growth is. Usually the profitability metric used here is FCF margin..."
