प्रदीपेप्रदीपं प्रज्वाल्य तमोनशाय यतमानः न्यायः

It takes origin from the attempt of chasing the darkness under a lamp by lighting a second lamp which again has darkness underneath it, and again to chase that darkness another lamp is lighted, and so on, and is used to indicate that efforts made for effecting what is impracticable always prove to be fruitless.