Yōga Sūtra 1.20

श्रद्धावीर्यस्मृतिसमाधिप्रज्ञापूर्वक इतरेषाम्।

Equilibrium state (samadhi) with knowledge and others is obtained by keen interest with reverence, bravery, and introspection.

For obtaining any equilibrium state keen interest with reverence, bravery and memory are stated as pre-requisite. Here smruti is to be understood to mean recalling past events with the intention of introspection.