fall behind — to drop or descend under the force of gravity, as to a lower place through loss or lack of support.
fail — to fall short of success or achievement in something expected, attempted, desired, or approved: The experiment failed because of poor planning.
lose — to come to be without (something in one's possession or care), through accident, theft, etc., so that there is little or no prospect of recovery: I'm sure I've merely misplaced my hat, not lost it.
surrender — to yield (something) to the possession or power of another; deliver up possession of on demand or under duress: to surrender the fort to the enemy; to surrender the stolen goods to the police.