Why Lennie's death is unavoidable ?

Lennie's death in general, or Lennie's death as a result of his actions. Lennie had been in trouble prior to arriving at the ranch. People didn't understand that he was mentally challenged..... he was big and strong, but people didn't see that he was like a big kid. In the end, Lennie's death was unavoidable because Curley's wife had been murdered..... and Lennie had killed her. George knew he'd be killed, so in order to save him suffering at the hands of the men who would torture and hand him..... he killed him quickly.... instantly.