The Lem scene is the most heartbreaking thing ever. You can see the anguish is Shanes face and when he turns around to face Lem after the act and for both to know what he did is emotional beyond belief.
But every bad thing that happened to that team ultimately was a mistake from Shane being Rash and as you have said; not being as clever as Vic and thinking ahead.
Do you blame Shane more for Lem or Vic more for Ronnie? Thats an interesting question.