Hope:

It was hope undid them. Hope, and the certainty that Providence had made them suffer enough for their dreams. They'd lost so much already along the trail--children, healers, leaders, all taken--surely, they reasoned, God would preserve them from further loss, and reward their griefs and hardships with deliverance into a place of plenty.
    -Clive Barker, Everville

Hope is dangerous. It'll cause you to take on way more than you can handle. Too much land, too big of a move, too big of a leap, too much of whatever. The only hope is to have no hope.