You're assuming nothing like the Nikkei index from 1989 - present will ever happen to a US stock index. I agree with you but stock market growth is not a law of

You're assuming nothing like the Nikkei index from 1989 - present will ever happen to a US stock index. I agree with you but stock market growth is not a law of nature. Other tactics (e.g. dollar cost averaging) are also needed to ensure a secure retirement.