Two Hundred Dollars and a Bus Pass - S1-E8
Stupidity: Two police officers and a physician find an injured woman in a lab. The officers attend to the woman while the physician calls for EMTs. Wouldn't it be better if the physician looked after the injured person while the officers called for help?
Stupidity: Characters repeatedly make note of how hard to kill the Wraith are, but sometimes, especially in the final episode(s) of season 1, they go down easily in a few bullets each, and then don't even regenerate as the characters turn their attentions elsewhere.