किं दुष्करं नराणां यन्मनसो निग्रहः सततम् ।को ब्रह्मचर्यवां स्यात्यश्चास्खलितोर्ध्वरेतस्कः ॥ ५३ ॥
In plain words
What is genuinely hard for a human being? Holding the mind in check — and holding it without a break. And who truly lives brahmacarya? The one whose vital seed never spills, but rises.
Close to the Sanskrit
What is hard to do for men? That which is the restraint of the mind, continuously. Who would be one endowed with brahmacarya? He whose seed is unspilled and turned upward.