Those who have not developed this mind, which is recondite and contains the whole sum of dharmas, wander the compass in vain trying to attain happiness and destroy suffering.
Therefore I should manage and guard my mind well. If I let go of the vow to guard my mind, what will become of my many other vows?
In the same way that someone in the midst of a rough crowd guards a wound with great care, so in the midst of bad company should one always guard the wound that is the mind.
[...from Chapter V of The Bodhicaryavatara by Santideva, v. 17-19]