SB 10.85.44

idam ittham iti prāyas
 tava yogeśvareśvara
na vidanty api yogeśā
 yoga-māyāṁ kuto vayam
Word for word: 
idam — this; ittham — characterized like this; iti — in such terms; prāyaḥ — for the most part; tava — Your; yoga-īśvara — of the masters of yoga; īśvara — O supreme master; na vidanti — they do not know; api — even; yoga-īśāḥ — the masters of yoga; yoga-māyām — Your spiritual power of delusion; kutaḥ — what then of; vayam — us.
Translation: 
What to speak of ourselves, O Lord of all perfect yogīs, even the greatest mystics do not know what Your spiritual power of delusion is or how it acts.
Purport: 

Systematic understanding of something should include knowledge of both its svarūpa, or essential identity, and also its viśeṣas, the attributes that make it different from other things. Māyā, the energy underlying all material existence, is more subtle than ordinary phenomena. Only God and His liberated devotees, therefore, can know its svarūpa and viśeṣa.