BITE OFF MORE THAN (ONE) CAN CHEW
to take on more work or responsibility than one can accomplish
1. Sue plans to oversee the construction of her new house at the same time that she has taken on a lot of volunteer work at her son’s school. I think she has bitten off more than she can chew.
2. They can’t keep up with the number of classes they’re taking at the university. They bit off more than they can chew.
BEAT A DEAD HORSE
to argue or pursue a point or topic without the possibility of success
1. They should give up trying to argue with the boss on that subject. They’re beating a dead horse.
2. The boy kept asking for a motorcycle, but his mother told him he could not have one and she would not change her mind. She told him he was beating a dead horse.
BEAT (SOMEONE) TO THE PUNCH
to do something before someone else does it
1. They decided to make an offer to buy the house, but when they did, they found that someone else had already bought it. Someone beat them to the punch.
2. Linda was going to invite him out to lunch but he beat her to the punch. He invited her before she had a chance to ask him.