The more someone talks, the more they reveal about themselves and the more they reveal about the way something has affected them.
The power of narrative sort of defines something forever and ever.
People are so complex that you can't possibly know anybody in 90 minutes.
People are interested in examining the way we consume narratives.
You can't possibly spend a lifetime with anybody and know them.
If the participants regret participating, then you won't have something that reveals some greater truth about human condition or allow some other perspective. You need people to want to be there so they can talk at length and want to continue talking to you.