If you are lead, then you should lead. If you lose faith, they lose faith. That being said, faith won't magically fix everything. If you are unable to make it,

If you are lead, then you should lead. If you lose faith, they lose faith. That being said, faith won't magically fix everything. If you are unable to make it, then figure out what you can deliver and then tell your manager/product owner. Deliver the "bad news" with a constructive alternative. Cut away some features and then going forward be ruthless about scope creep. Urgent thing CAN come, but then others needs to be removed.