Bhagavad Gita Chapter 06, Text 08

Bg 6.8

kuta-stho vijitendriyah
yukta ity ucyate yogi

Word for word: 
jnana — by acquired knowledge; vijnana — and realized knowledge; trpta — satisfied; atma — a living entity; kuta-sthah — spiritually situated; vijita-indriyah — sensually controlled; yuktah — competent for self-realization; iti — thus; ucyate — is said; yogi — a mystic; sama — equipoised; lostra — pebbles; asma — stone; kancanah — gold.

Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
A person is said to be established in self-realization and is called a yogi [or mystic] when he is fully satisfied by virtue of acquired knowledge and realization. Such a person is situated in transcendence and is self-controlled. He sees everything – whether it be pebbles, stones or gold – as the same.

Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Book knowledge without realization of the Supreme Truth is useless. This is stated as follows:

atah sri-Krishna-namadi
na bhaved grahyam indriyaih
sevonmukhe hi jihvadau
svayam eva sphuraty adah

“No one can understand the transcendental nature of the name, form, quality and pastimes of Sri Krishna through his materially contaminated senses. Only when one becomes spiritually saturated by transcendental service to the Lord are the transcendental name, form, quality and pastimes of the Lord revealed to him.” (Bhakti-rasamrta-sindhu 1.2.234)

This Bhagavad-gita is the science of Krishna consciousness. No one can become Krishna conscious simply by mundane scholarship. One must be fortunate enough to associate with a person who is in pure consciousness. A Krishna conscious person has realized knowledge, by the grace of Krishna, because he is satisfied with pure devotional service. By realized knowledge, one becomes perfect. By transcendental knowledge one can remain steady in his convictions, but by mere academic knowledge one can be easily deluded and confused by apparent contradictions. It is the realized soul who is actually self-controlled, because he is surrendered to Krishna. He is transcendental because he has nothing to do with mundane scholarship. For him mundane scholarship and mental speculation, which may be as good as gold to others, are of no greater value than pebbles or stones.