An intelligent person, expert in perceiving the world around him and in applying sound logic, can achieve real benefit through his own intelligence. Thus sometimes one acts as one’s own instructing spiritual master.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
आत्मनो गुरुरात्मैव पुरुषस्य विशेषतः । यत्प्रत्यक्षानुमानाभ्यां श्रेयोऽसावनुविन्दते
ātmano gururātmaiva puruṣasya viśeṣataḥ | yatpratyakṣānumānābhyāṃ śreyo'sāvanuvindate
SB 11.7.20