I don't know if it's specifically 16+ years down the line. However, my understanding is that the model for most writers (i.e. those who don't become famous) is

I don't know if it's specifically 16+ years down the line. However, my understanding is that the model for most writers (i.e. those who don't become famous) is to keep writing books and develop a fanbase over time and/or gain a little over time from each book in the hope that eventually the aggregate is enough to switch to writing full time.