Idiom meaning, usage examples, facts

1. Henry tried everything he could think of to change Martha’s mind, even tried things that he knew wouldn’t work. He knew he was grasping at straws
2. The thief told the judge one excuse after another. It was obvious that he was desperate and grasping at straws.

The expression suggests that whereas grasping a rope might succeed in saving one’s life, grasping at straws (grass) is a desperate and probably useless attempt to hold on.