Chapter 4 · Knowledge and Renunciation of Action · Krishna said
Bhagavad Gita 4.40 — Doubt destroys
अज्ञश्चाश्रद्दधानश्च संशयात्मा विनश्यति। नायं लोकोऽस्ति न परो न सुखं संशयात्मनः ॥
ajñaścāśraddadhānaśca saṃśayātmā vinaśyati | nāyaṃ loko'sti na paro na sukhaṃ saṃśayātmanaḥ ||
Meaning
The ignorant person without faith, who is full of doubt, is ruined. For the doubting mind there is no happiness, neither in this world nor the next.