This tale is from Yoga Vasishtha, where Rama's mentor advises him to gain true strength unlike asuras Dama, Vyala, and Kata. In the inevitable battle between devas and asuras, the latter were winning, not just once but in every battle. Brahma offers devas this solution: he advises them to keep attacking and withdrawing. This constant on-off ruse will make the asuras believe themselves to be invincible. This will create their downfall by strengthening the I-factor. Once this I-factor becomes strong, the asuras will start suffering a steady down-fall because this sort of success also generates deep fear (of failure), a compulsive and self-destructive obsession with superficial worldly pleasures which will dissipate their energies, which will drag their mental powers further down. They will become depressed, agitated, they will destroy themselves. To have true strength, advises Vasishtha, you have to constantly nip the obsessive I-factor, focusing on the work at hand instead of the false ego. Such pure focus will ensure success, while the sort of success bred by the ego is sure to collapse. The mythical devas and asuras, of course, stand for our own positive and negative selves, while the battle success being discussed is related to any work we undertake.
This `energy lock' has other names, including shanmukhi mudra. It is simple to instruct but difficult to practice, requiring mental stamina and discipline.
Sit cross-legged. Eyes shut. Lift hands, elbows straight out. Plug ears with each thumb. Use other fingers to shut the other `gateways': place index finger gently on shut eyes, middle finger tips on nostrils – do not shut the nostrils, just place the fingers gently. Place ring finger and little finger on top of upper and lower nostrils respectively. Breathe naturally, hearing the subtle physical sounds that this complete lock provides.
Science speak: This is a powerfully involuting and introverting practice. Avoid if shy or depressed. It helps direct mental focus more keenly inwards, making your watch your inner talk more objectively and critically. It is also a spiritual practice, that prepares you for advanced nada yoga of sound. It is said to relax the facial nerves and muscles. It is therapeutic in anger management.
Wisdom from the ages: `The effects of action (for a yogi) are immediate or delayed (as he desires). By samayama (complete attention through focus, mediation and samadhi or merger), the yogi will gain foreknowledge of their final fruits.' From Patanjali's Yoga Sutras.