This verse is from the Bhagavad Gita, Chapter 6, Verse 34. It is written in Sanskrit and translates to English as follows:
chañchalaṁ hi manaḥ kṛiṣhṇa pramāthi balavad dṛiḍham
tasyāhaṁ nigrahaṁ manye vāyor iva su-duṣhkaram || 34 ||
"Hey Krishna! The mind is extremely fickle, restless, extremely strong and determined. I consider controlling it as difficult as controlling the wind."
This verse of Bhagavad Gita tells us how the nature of the mind can be a big obstacle in human life. It is clear from this statement of Arjun that the biggest obstacle in the path of self-control and meditation is the mind. The biggest challenge is the fickleness of the mind. Lord Krishna explains the ways to control it in the following verses.
Chanchalam – restless, restless
Hi – Definitely, actually
Manah: – Mind
Krishna – O Krishna! (Addressing Lord Krishna)
Pramathi – destabilizing, turbulent
balavad – Extremely strong
dridham – firm, unwavering
tasya – of his (mind)
aham – I am
Nigraham – to control, to subdue
Manye – I believe
Vayor: – of the air
ive – similar to
Sudushkaram – extremely difficult