Chapter-16, Verse 3

Ashtavakra Gita Verse 16.3:

आयासात्सकलो दुःखी नैनं जानाति कश्चन ।

अनेनैवोपदेशेन धन्यः प्राप्नोति निर्वृतिम् ॥ ३ ॥

From mental effort, everyone is miserable, but no one knows this.

By just this instruction alone, the fortunate one attains peace.

The root cause of suffering is the exertion of the mind and senses in pursuit of material objects and pleasures. Such effort is based on ignorance of one's True Nature as the eternal soul, which is ever blissful and free from all desires. 

Ashtavakra advises that one should give up all such endeavors and simply follow the essence of Vedanta, or the knowledge of the Self. By doing so, one can attain the state of nirvriti, or cessation of all outward tendencies of the mind and attainment of Supreme Peace. 

- The Isha Upanishad (Verse 7) says:

यस्मिन् सर्वाणि भूतानि आत्मैवाभूद् विजानतः । तत्र को मोहः कः शोक एकत्वमनुपश्यतः ॥

In whom all beings are known as the Self alone; What delusion or grief can there be for him who sees oneness? 

- The Bhagvad Gita says:

कर्मण्येवाधिकारस्ते मा फलेषु कदाचन ।

मा कर्मफलहेतुर्भूर्मा ते संगोऽस्त्वकर्मणि ॥

Your right is to work only, but never to its fruits; Let not the fruits of action be your motive, nor let your attachment be to inaction.

- The Vivekachudamani (Verse 20), summarizes the main doctrine of Advaita Vedanta thus:

ब्रह्म सत्यं जगन्मिथ्या जीवो ब्रह्मैव नापरः ।

अनेन वेद्यं सच्छास्त्रमिति वेदान्तडिण्डिमः ॥

Brahman is real, the world is false, the individual soul is none other than Brahman. By this alone is known the true scripture, this is the verdict of Vedanta.