B.G 3.38, 39, and 40

धूमेनाव्रियते वह्निर्यथाऽदर्शो मलेन च। यथोल्बेनावृतो गर्भस्तथा तेनेदमावृतम् ॥३८॥

Just as fire covered by smoke, mirror covered by dirt, and the womb covered by the embryo, is not seen, similarly, this (supreme being, the inner heart and the being) are covered by that (desire).

आवृतं ज्ञानमेतेन ज्ञानिनो नित्यवैरिणा। कामरूपेण कौन्तेय दुष्पूरेणानलेन च ॥३९॥

O son of Kunti, Arjuna, This knowledge of the knower is covered by the eternal enemy in the form of desire that is difficult to satisfy, and is like a fire that does not stay as is.

इंद्रियाणि मनो बुद्धिरस्याधिष्ठानमुच्यते। एतैर्विमोहयत्येष ज्ञानमावृत्य देहिनम् ॥४०॥

It is said that the senses, the mind, and the intellect are the places where it resides. By these desire envelops the knowledge of the embodied one.

Gīta Tātparya 3.38, 39 and 40

Desire is not only difficult to satisfy, it can never be satisfied. Hence, words 'duṣpūrēṇa' and 'anala' are used respectively.

"अखिलप्रेरको विष्णुः ब्रह्माध्याः तदवान्तराः। असुरा अशुभेष्वेव कामादेरभिमानिनः॥ तत्र कामः कालनेमिः सर्वं धूममलोल्बवत्। शुभमध्याधमजनं क्रमादावृत्य तिष्ठति॥ महाशनस्य तस्येदं नालं तेनानलोऽग्निवत्। भुञ्जान इंद्रियाविष्टो ज्ञानास्त्रेणैव दह्यते॥"

इति ब्रह्मतर्के।

"Lord Vishnu is the inspirer of everything. Within it's ambit are Brahma and others. The Demons preside over the inauspicious like desires, etc. The demon named 'Kalanemi', the time, rules over desires, like a drifting smoke, covering all types of people: the auspicious, the middle, and the lower. This great devourer (mahāśana) consumes, engaged in sensory pleasures, never feeling satisfied (anala), like a fire. He can be destroyed only by the weapon of knowledge."

- states Brahma Tarka

ज्ञानावरणरूपेण इदमावृणोतीति आवृतं ज्ञानमिति पुनराह। न केवलं दुष्पूरो नालमिति मन्यते चेत्यनलः।

The way it (desire) covers knowledge, similarly it (desire) also covers (senses) is conveyed by using the words 'jñānamāvr̥tya' again (3.40). It is not a repeatition. Not only it is 'duṣpūrēṇa', i.e. it is difficult to satisfy, it is 'anala' i.e. it cannot be satisfied, hence it is compared to fire.

'अग्नेरप्यनलः कामो यन्नालमिति मन्यते'

इति च ॥३७-४०॥

"The way fire is never satisfied, desire also can never be satisfied, thus wise believe."

- states ancient proverb.