10.15 You alone know yourself Arjuna speaks

स्वयमेवात्मनाऽत्मानं वेत्थ त्वं पुरुषोत्तम
भूतभावन भूतेश देवदेव जगत्पते

swayam evātmanātmānaṁ vettha tvaṁ puruṣhottama
bhūta-bhāvana bhūteśha deva-deva jagat-pate

You alone know yourself by yourself, highest person, source of beings, lord of beings, god of gods, ruler of the world.

Explanation

You alone know yourself by yourself.

Which is the conclusion 10.2 forces. If nothing can locate its own source, then the only witness available is the source itself.

Arjuna has worked this out rather than been told it, and it is the ground for the request he makes next: he cannot find out, so he has to ask.