I don't think anyone can really know the answer to something so personal as why Chaney Jr. drank. Like others, we can make guesses like the pressure of living in the shadow of his superstar father. But I think he must have had some natural predilection for drinking since it apparently started when he was very young. When I met serial expert Alan Barbour many years ago and talked to him about Chaney, he said that director Spencer Gordon Bennet told him Chaney was drunk during most of the filming of his first serial THE LAST FRONTIER in 1932.