S. R. Faruqi:

Ghalib has written to Chaudhari 'Abd ul-Ghafur Surur (in 1859 or 1861),

'The moving-along of a verse is a task for limbs and bodily parts. A heart is needed, a mind is needed, relish is needed, ardor is needed, longing is needed. Where would I get this equipment, such that I would compose a verse?'

It's possible that he might have had before him the second line of Mir's verse from the second divan [{896,1}]:

baa;G ko sabz hu))aa ab sar-e gulzaar kahaa;N
dil kahaa;N vaqt kahaa;N ((umr kahaa;N yaar kahaa;N

[although the garden has become green, now where is a mind/head for the garden?
where is the heart, where is the time, where is the lifetime, where is the beloved?]

But it's also possible that Ghalib might have had in mind the present verse as well.

The theme of the verse is entirely new; in the second line especially, he's composed an entirely fresh idea. From composing poetry, one's life is worn out. Although this task is not physical, and in it there's no bodily damage, a good verse comes into being only after much inner bloodshed. In this process not only is pressure put on the mind, but in bringing into action the energies of experience, memory, and thought, one feels as though the lifetime itself is being used up. Iqbal has well said [in the third stanza of Masjid-e Qurtubah],

mu((jizah-e fan kii hai ;xuun-e jigar se namuud

[the manifestation of miracles of art, is from the blood of the liver]

In the second line, the suggestion is that poetry-composition is a personal act no doubt, but a verse is everybody's property. If the poet composes a verse, then it's as if he does a service to God's creatures, and does a disinterested service. Now, when there remains no more strength in his heart and power in his mind, poetry-composition will become a form not only of harming his life, but rather of ending it. For this reason he now keeps his own survival in view, and treats poetry-composition as something that has been renounced.

One additional point is that the person who is lost only in himself, cannot compose verses. For poetry, it's also necessary to have what Hali has called 'contemplation of the universe'.

FWP:

SETS == POETRY
MOTIFS
NAMES
TERMS == THEME

The first line may be asking 'Who has the mental energy to compose poetry?' or else 'Who has the pride or arrogance to compose poetry?'; and the barrier may be anything from physical weakness (including fainting fits or swoons), to 'imbecility' (see the definitions above). It's a fine inventory of possibilities!

And of course, the poet's thought may 'remain his own' nowadays because he withholds it from the clamoring fans who want to share it-- or else because nobody really gives a damn. Perhaps the only way he ever shared his thoughts with anyone was by composing poetry, so now without that he is truly alone.

Note for grammar fans: In the second line, what about that hame;N ? I'm not quite sure how it should fit into the line. But the general intent is clear enough.