SB 3.26.27

vaikārikād vikurvāṇān
 manas-tattvam ajāyata
yat-saṅkalpa-vikalpābhyāṁ
 vartate kāma-sambhavaḥ
Synonyms: 
vaikārikāt — from the false ego of goodness; vikurvāṇāt — undergoing transformation; manaḥ — the mind; tattvam — principle; ajāyata — evolved; yat — whose; saṅkalpa — thoughts; vikalpābhyām — and by reflections; vartate — happens; kāma-sambhavaḥ — the rise of desire.
Translation: 
From the false ego of goodness, another transformation takes place. From this evolves the mind, whose thoughts and reflections give rise to desire.
Purport: 

The symptoms of the mind are determination and rejection, which are due to different kinds of desires. We desire that which is favorable to our sense gratification, and we reject that which is not favorable to sense gratification. The material mind is not fixed, but the very same mind can be fixed when engaged in the activities of Kṛṣṇa consciousness. Otherwise, as long as the mind is on the material platform, it is hovering, and all this rejection and acceptance is asat, temporary. It is stated that he whose mind is not fixed in Kṛṣṇa consciousness must hover between acceptance and rejection. However advanced a man is in academic qualifications, as long as he is not fixed in Kṛṣṇa consciousness he will simply accept and reject and will never be able to fix his mind on a particular subject matter.