watch it: “Scott Bakula - Imagine”

Yeah, this is the scene that I always associate with the show when it comes up. At the time this aired, I was probably in middle school, and not having come from an especially culturally literate family, this scene was my first exposure to the song. It led me to a later interest in John Lennon.

Sometimes I think "Don't tell her" is the most evocative statement about the '60s that I've ever heard.

This was easily the best episode Quantum Leap ever had.

I think even worse than the girl's reaction is Sam's reaction: He finally convinces the family that he knows the future but Al still tells him that the future remains unchanged -- brother still dead in Vietnam and sister still married to an abusive alcoholic. This is a crusing episode.

He finally convinces the family that he knows the future but Al still tells him that the future remains unchanged -- brother still dead in Vietnam

As I recall, though, he DOES leap in the very next episode to Vietnam and DOES save his brother's life. (At the expense of saving Al from five years in POW camp.)