When my wife starts to look good, I go home

A man walks into a bar and orders a shot, then he looks into his shirt pocket and orders another one.

After he finishes, he looks into his pocket again and orders another shot. 

The bartender is curious and asks the man why he looks into his pocket before ordering each shot. 

The man replies, 

“I have a picture of my wife in my pocket, and when she starts to look good, I go home.”