So OP was making 300k (roughly standard for a mid-level engineer in the Bay Area at about 20+ different companies here) and dumping 160k of it into index funds

So OP was making 300k (roughly standard for a mid-level engineer in the Bay Area at about 20+ different companies here) and dumping 160k of it into index funds every year. With the market basically doubling over the past 8 years with no inflation, and those returns compounded, it's clear to see how he got to $2m. This doesn't account for any returns on company stock OP held on to (tech companies have basically doubled the return of the S&P over the past 10 years). Whether you could replicate OP's experience over the next 10 years, is debatable.