Money is a tool to help one to have the choice to be FIRE. There is only this amount of money which one can make in the course of the full time. I am of view that one should go for early retirement when he/she has saved the sufficient money to sustain himself/herself in life. This will include the own saving and CPF savings in Singapore context. The 4% rule is sufficient to help one to estimate the so-called FIRE figure. If one has saved 25 times of his/her annual expense, I am of view that the individual is well set to quit his/her full-time employment.