आत्मौपम्येन सर्वत्र समं पश्यति योऽर्जुन ।सुखं वा यदि वा दुःखं स योगी परमो मतः॥
ātmaupamyena sarvatra samaṃ paśyati yo ’rjunasukhaṃ vā yadi vā duḥkhaṃ sa yogī paramo mataḥ
Word by word
The verse says
Whoever sees the same everywhere by the likeness of himself, Arjuna — whether it is happiness or suffering — that practitioner is held to be the highest.
In plain words
Ātmaupamyena — by the likeness of oneself.
You already know what suffering is. You have the sample.
And this verse says that sample is how you know about everybody else's.
Where you've felt this · in community
You hear a stranger describe exactly the fear you had last year, and your whole body answers before your mind does. You do not have to work out what they mean. You already know.
Going deeper
This is the golden rule arriving as perception rather than as instruction, and the difference matters.
Most traditions put it as a command: treat others as you would be treated. Here there is no command. It is a description of what someone sees — ātmaupamyena, by comparison with oneself — and the conduct is left to follow.
That ordering is consistent with everything the Gita does. It keeps declining to legislate behaviour and keeps describing the position a person is standing in, on the grounds that conduct is downstream.
And notice that happiness is included alongside suffering. Sharing someone's pain is the familiar half. Being equally able to feel their good fortune as your own is harder, and it is the half that envy destroys first.
Paramo mataḥ — held to be the highest. Of everything described in a chapter full of technique, the summit is this, and it requires no posture at all.