Curious Caving In

Daddy first started smoking when he was 13:  he'd roll his own oak leaf cigarettes.  But that soon turned into the "real" thing, and continued till '65 (when the gov't. started its anti-smoking campaign, but of course Daddy swore "it had nothing to do with the feds' nonsense!  It was just time to quit, that's all!").  I remember several years later he said, "Cheez, I didn't know just HOW sick I felt till after I quit and felt so much BETTER!" 

I was amazed, when in '83, I came home for a visit, and there he was, smoking again (albeit only outside the house).  What had happened to my sensible father?  How can someone, after that many years of happy abstention, plummet back into the snare?  18 years of healthy living tossed away like an old stub.  Sure, the woman who eventually became my 2nd stepmother, she dragged him from one cocktail party to the next, where they smoked like the crematoria, but why would that have enticed him back into s.th. he had left behind as abhorrent?