नास्ति बुद्धिरयुक्तस्य न चायुक्तस्य भावना।न चाभावयतः शान्तिरशान्तस्य कुतः सुखम्॥
nāsti buddhir-ayuktasya na cāyuktasya bhāvanāna cābhāvayataḥ śāntir aśāntasya kutaḥ sukham
Word by word
The verse says
Without that joining there is no understanding, and no steady attention either. Without attention there is no peace - and where is happiness for a person with no peace?
In plain words
The same chain as verse 62, running the other way.
No joining, no understanding. No understanding, no steady attention. No attention, no peace. No peace - and then the question at the end, which is not really a question.
Where would happiness come from?
Where you've felt this · in growing older
Your cousin chases the better holiday, then the better flat, then the right job. Each one arrives and works for a fortnight. The chasing is not the problem. There is nowhere in him for any of it to land.
Going deeper
Four negatives in a row, and the cumulative effect is the argument.
Ayuktasya - of the unjoined, the one not in yoga. Everything in the verse hangs off that first condition, and the chain is strictly ordered: joining, then understanding, then bhāvanā - sustained attention, the capacity to hold something steadily in mind - then peace, then happiness.
The ordering is the teaching. Happiness sits at the far end, four steps downstream, and it cannot be reached directly. Every attempt to grab it from where you are standing skips the chain.
This is the Gita's answer to a question everyone asks, and it is not a comfortable one. You do not get peace by arranging for peaceful circumstances. Peace is a consequence of attention, and attention is a consequence of understanding, and understanding requires being joined to something steadier than your own preferences.
And there is a structural joke in the placement. This verse sits between two of the most beautiful images in the chapter - the boat in the wind, and the ocean. Krishna makes the dry argument first and then shows you what it looks like.