SB 1.6.19

didṛkṣus tad ahaṁ bhūyaḥ
 praṇidhāya mano hṛdi
vīkṣamāṇo ’pi nāpaśyam
 avitṛpta ivāturaḥ
Synonyms: 
didṛkṣuḥ — desiring to see; tat — that; aham — I; bhūyaḥ — again; praṇidhāya — having concentrated the mind; manaḥ — mind; hṛdi — upon the heart; vīkṣamāṇaḥ — waiting to see; api — in spite of; na — never; apaśyam — saw Him; avitṛptaḥ — without being satisfied; iva — like; āturaḥ — aggrieved.
Translation: 
I desired to see again that transcendental form of the Lord, but despite my attempts to concentrate upon the heart with eagerness to view the form again, I could not see Him any more, and thus dissatisfied, I was very much aggrieved.
Purport: 

There is no mechanical process to see the form of the Lord. It completely depends on the causeless mercy of the Lord. We cannot demand the Lord to be present before our vision, just as we cannot demand the sun to rise whenever we like. The sun rises out of his own accord; so also the Lord is pleased to be present out of His causeless mercy. One should simply await the opportune moment and go on discharging his prescribed duty in devotional service of the Lord. Nārada Muni thought that the Lord could be seen again by the same mechanical process which was successful in the first attempt, but in spite of his utmost endeavor he could not make the second attempt successful. The Lord is completely independent of all obligations. He can simply be bound up by the tie of unalloyed devotion. Nor is He visible or perceivable by our material senses. When He pleases, being satisfied with the sincere attempt of devotional service depending completely on the mercy of the Lord, then He may be seen out of His own accord.