In series 2, episode 4 of Red Dwarf, Stasis Leak, the post-apocalypse crew find a way to travel back in time to the Dwarf before the crew was wiped out and Lister resolves to freeze Kristine Kochanski in a stasis booth so he can live with her on the empty ship.
The episode ends with Lister discovering Kochanski is married to a (presumably alternative) future Lister, he is not able to take her with him to the future.
It's also established in the same episode that Lister really misses his drinking buddy, Olaf Peterson. He's thrilled to meet him, alive and well, in the past.
The question is this, after finding out that he can not save Kochanski from the fatal leak that wiped out the crew, why didn't Lister try to save Petersen (or one of his other buddies such as Chen or Selby) from the event instead?
Bonus question: Why didn't he try to stop the fatal event, either?