Sududdasaṃ sunipuṇaṃ, yatthakāmanipātinaṃ;
Cittaṃ rakkhetha medhāvī, cittaṃ guttaṃ sukhāvahaṃ.
It is so difficult to detect the true nature of the mind. The mind is extremely subtle and seizes whatever it desires. A guarded mind brings happiness.The mind is so difficult to subdue. It is unreliable. It seizes whatever it desires. Good indeed, it is to tame such a mind. A tamed mind brings happiness.
Read all the verses in the chapter of The Mind on SuttaFriends.org in Pali and English.