If you were a kid watching TV in the 1980s and 1990s, you probably saw a fair number of “Very Special Episodes,” when the usual blissful bubble of the sitcom world was punctured by real-world issues for a half-hour. Drugs, drinking and driving, stranger danger, even AIDS. But never fear, all would be resolved by episode’s end. (Sometimes the material was so heavy, it required a two-parter.) So why did such a mainstay for a generation of families disappear? And how much was Seinfeld to blame? Mo talks with entertainment writer Jessica Shaw and the late great Norman Lear about the birth, life and death of a cultural phenomenon.