…if you develop the habit… of calling as by a mantra, of repeating a word, that has an extraordinary effect. You choose your mantra; or rather, one day it comes to you spontaneously in a moment of difficulty. At a time when things are very difficult, when you have a sort of anguish, anxiety, when you don’t know what is going to happen, suddenly this springs up in you, the word springs up in you. For each one it may be different. But if you mark this and each time you face a difficulty you repeat it, it becomes irresistible… The best is when the word comes to you spontaneously: you call in a moment of great difficulty (mental, vital, physical, emotional, whatever it may be) and suddenly that springs up in you, two or three words, like magical words. You must remember these and form the habit of repeating them in moments when difficulties come. If you form the habit, one day it will come to you spontaneously: when the difficulty comes, at the same time the mantra will come.

Ref: Question and Answers 1950-1951