I started following Henry Hebeler's articles in his www.analyzenow.com
website about 5 years before I retired. I bought the book after retirement and read it like a textbook, concentrating on those chapters that show how to do something that I'm interested in at the time. The website articles are somewhat easier to read than the book but both are highly informative.
I have an engineering background and can follow the feedback arguements but have been primarily happy to note that my income is somewhat north of my expenses allowing me to be pretty casual about adjusting for the ups and downs of the market.
This is what I got from his writings; Mr Hebeler correctly recommends that (1) you need savings so you can have investments and (2) that you need to take care not to outlive your assets. His answers include the recommendation to (1) continue to save in the early years after retirement and to (2) project into the future using analyses taking into account inflation and turmoil in the markets. He offers analyses similar to FIRE-Calc and useful spreadsheets, many of which are free.
He especially concentrates on the impact of being in retirement for a long time - something that is of particular significance to the early retirement crowd.
I always learn something when I read from his website!