to get tired of (doing); to lose interest in
to tire of; to lose interest in; to be too much for one; to find unmanageable; to be beyond one's control; to not know what to do with
to be at a loss; to think and think but get nowhere; to fail to come up with a good idea
to be at a loss how to continue; to become disheartened
to think something over and over; to rack one's brains; to be at a loss
to lose the attacking initiative
to give up searching (for someone or something)