Go straight to jail, do not pass go, do not collect £200

I played a few cheap sit'n'goes on Pokerstars yesterday, and performed pretty well in all of them, but didn't win any. Thoughout the session I was haunted my runner-runner straights. I would have something fairly strong, you know, a pair of aces or a pair of kings? Completely non-threatening flops, my all-in called by some idiot with J-7, then 9-T on turn and river to go with the 8 on the flop. What are these guys on?