Why is Candy worried that he will be fired?
There was no such thing as mandatory Workmen's Compensation insurance in the 1930s. Candy was given $250 when he lost his hand in a farm machine, and he has been kept on as a sort of janitor for the past four years. But he knows that his days are numbered and that he would find it impossible to get any other employment if he were fired. He tells George and Lennie:
"I got hurt four years ago. They'll can me purty soon. Jus' as soon as I can't swamp out no bunkhouses they'll put me on the county. Maybe if I give you guys my money, you'll let me hoe in the garden even after I ain't no good at it. An' I'll wash dishes an' little chicken stuff like that."
Being put on the county probably meant being put in a home for indigents, where Candy would be treated almost like a prisoner. To him, the idea of living on a little farm seems like a miraculous alternative. He is ecstatic when George agrees to take him on as a co-owner of the little farm he is planning to buy with Lennie. Candy can't think about anything else or talk about anything else up until the time that he discovers Curley's wife lying dead in the barn. Then he knows that he has lost his only hope of retaining a shred of dignity and independence. He speaks to the dead girl as follows:
"You God damn tramp," he said viciously. "You done it, di'n't you? I s'pose you're glad. Ever'body knowed you'd mess things up. You wasn't no good. You ain't no good now, you lousy tart."
One of the problems with Steinbeck's characters is that they can't seem to manage for themselves. They are handicapped by ignorance and low-grade intelligence. Slim is an exception. George is also a possible exception, and he may go on to have a better life without being burdened by Lennie. For most of the bindle stiffs there is no hope. They are overworked and underpaid, and like Candy they are cast out when they are no longer exploitable.
Candy is worried that he will be fired because he is old and only has one hand. Even though he lost the hand on the ranch, he knows that as soon as he can no longer do his job he will be fired. He feels that he, like his dog, will be seen to be not good for anything anymore. This is the reason he is so intent upon joining Lennie and George in buying the farmhouse and gaining their independence.