अज्ञश्चाश्रद्दधानश्च संशयात्मा विनश्यति।नायं लोकोऽस्ति न परो न सुखं संशयात्मनः॥
ajñaś cāśraddadhānaś ca sanśayātmā vinaśyatināyaṃ loko ’sti na paro na sukhaṃ sanśayātmanaḥ
Word by word
The verse says
The one who does not know, who does not trust, whose self is made of doubt - he is lost. For the one made of doubt there is no this world, no other one, and no happiness.
In plain words
The counter-case, and it is the harshest sentence in the chapter.
Three conditions: not knowing, not trusting, and saṁśayātmā - a self made of doubt.
And the verdict has three parts: not this world, not the next, and no happiness anywhere.
Where you've felt this · in growing older
Your uncle spends forty years unable to commit to any of it - no job, no city, no person held for long. He was never wrong about anything, either. He also never got to live in a single one of the lives he examined.
Going deeper
The phrasing is the thing to notice: saṁśayātmā - one whose very self is doubt. Not someone who has doubts.
That distinction carries the verse, and it is the difference between a state and an activity. Doubting is how anyone thinks. Being made of doubt is a condition in which nothing can ever be tested, because testing means going ahead for a while without being sure.
The Gita is not attacking scepticism. Chapter 2 conceded that hearing all this leaves you not knowing it. And 4.34 prescribed paripraśna, thorough questioning. This is a text that keeps asking to be interrogated.
What it identifies is a posture in which the questioning has become the permanent address.
The severity still deserves to be named. Vinaśyati - he is destroyed - is a hard verdict, and readers are entitled to find it too hard. It is worth reading against 4.36, four verses earlier, where the worst of all wrongdoers is carried across. The Gita is stricter with the uncommitted than with the guilty, which is a strange and consistent feature of it.