Do we know how and when George and Lennie's dream came about?Was it from their childhood, or did they think up the dream when they were working at one of the farms?
George and Lennie's dream seems to have evolved from many sources during their time together, and is woven from their childhood memories and their experiences as itinerant labourers. It is made from the fabric of the American Dream to be successful and self sufficient with just hard work, determination and a little luck.
George uses the dream to placate Lennie and to soothe himself - it becomes like an evening prayer for the couple to see them through to the next day, and give them a reason to go on. It is clear that at some points George does not really believe it is likely to be true, and certainly by the end of their relationship it is no more than a distant fantasy.
George and Lennie's dream is not unique to the time or the sort of men carrying it. As Crooks says
" I seen hundreds of men come by on the road an' on the ranches, with their bindles on their back an' that same damn thing in their heads . . . every damn one of 'em's got a little piece of land in his head. An' never a God damn one of 'em ever gets it. Just like heaven. Ever'body wants a little piece of lan'. I read plenty of books out here. Nobody never gets to heaven, and nobody gets no land."
Sadly the dream is as unattainable for George and Lennie as it was for the thousands of migrant workers scouring the land for hope in the California dust bowl.