WHAT IT IS, WHAT IT ISN'T,
WHAT YOU NEED TO KNOW,
AND WHAT YOU CAN IGNORE.

1.The FIRE movement. F.I.R.E. (FIRE) is generally agreed to be an investment philosophy that emphasizes extreme saving of one's personal income in order to maximize investing.

The goal being to achieve an amount that essentially allows the individual the flexibility to permanently achieve financial independence. 
The F.I. part.

 Or to simply quit work altogether free to pursue whatever one wishes to pursue.
 The R.E. part.

O.K. 
What does that all mean? 
Basically FIRE adherents, and there’s lots of them, spend their earlier working years earning as much as they can and cutting their expenses to the very core to invest the absolute maximum (often in low expense index funds-good idea). This way, they can live off a very low withdraw rate.

The basic mathematical principles are these.

First; you must determine what your yearly income should be to live comfortable.

Second; that yearly income has to be multiplied by twenty-five.

Third; You should, from those savings be able to safely withdraw 4% per year, forever, without worrying about ever running out of money, theoretically.

Like anything, there are pros and cons involved.

Not mentioned so far is how to best invest this money to reach your goals. 
While there's no one best way, it does seem most investors involved overwhelming preferred low-cost index funds. 
Particularly the S&P 500 fund.

PROS: Assuming you have what it takes to embrace such an endeavor you can create the life of your Scroogiest dreams.
Once you recognize what that goal is and know how much per year that would mean you now know exactly, more or less, what you have to save and invest.
 It’s the certainty that’s most freeing to those of us struggling to put together our personal financial picture. 
While theres no guarantees in life, for many, this is the clearest possible path.

CONS: Admittedly FIRE is definitely not for everyone.
 In fact, it’s probably not for most people. 
Lifestyle creep is a real thing. Some people, especially younger participants may find FIRE isolating in that their ability to spend time, and money with friends, family, and coworkers over time.
 So consider those people most important in your life. 
Are you in this alone or is there a spouse/significant other involved?
In truth if only one person is committed than neither is committed.
 While the pros vastly outweigh the cons where FIRE is concerned, there are many ways to achieve financial independence so don’t feel pressured to follow any one specific path.