In Chapter Three, George tells Slim that if he was smart, he would not be working on someone else's land and would instead have a ranch of his own. This would enable him to reap the financial benefits that a ranch hand will never enjoy:
If I was even a little bit smart, I'd have my own little place, an' I'd be bringin' in my own crops, 'stead of doin' all the work and not getting what comes up outa the ground.
To put this comment into context, it comes after Slim calls Lennie a "cuckoo" and remarks that it is strange for George (a man who is "bright") to travel around with him. George's comment, therefore, is a defensive reaction because he feels that Slim has wrongly mocked Lennie's intelligence.
In addition, this comment demonstrates George's deeply-held desire to have his own ranch and to live off the "fatta the lan'." Although this dream seems impossible to achieve in Chapter Three, it does not stop George from believing in it.