After all the philosophy of oneness and all the meditation instructions, Krishna lands on something startlingly simple. The highest yogi is the one who feels other people's happiness and pain as if they were his own. That is it.
'Atmaupamya' means measuring by oneself. When someone else is hurting, the yogi thinks: 'If that were happening to me, I would suffer too.' When someone else is joyful, the yogi shares that gladness. This is not abstract philosophy. It is empathy — direct, gut-level, human.
Krishna calls this yogi 'parama' — the supreme, the highest. Not the one who can sit in meditation the longest. Not the one who knows the most scripture. The one who cannot see another person's pain without feeling it. That is the mark of the greatest yogi.