Shane was depicted like Shane: a short tempered, emotionally off-kilter, overly confident, shoot first ask questions later sort of guy. He has never been especially cunning so rushing into his half-baked plan when he spotted an opportunity(no matter how bad) is perfectly in character. I was able to guess his entire plot pretty much moment for moment after the preview at the end of the previous episode. They were very human actions from a very human character driven to extremes. From my perspective, it was always the foregone conclusion that Shane was going to make a move like this and would have to be put down.