The ETF would need to continue on its current path for a couple of decades.Hitting the million-dollar mark may be far-fetched by strictly saving money, but it's doable when you invest and rely on compound earnings to make it happen. It's the gift that keeps giving in investing.It doesn't take hitting big on the "next big thing," either. A simple exchange-traded fund (ETF) like the Vanguard Growth ETF (VUG 0.92%) has proven it can get the job done.Since it began trading in January 2004 and over the past deca ...