Totally depends. If it's 40, bee raining for 5 days and is still raining hard and I'm hypothermic I want a fire and I want it now. In fact, if we're talking short term survival (72 hours or less) I'll take fire most any time. I can certainly do a lot with a knife during that time, but I can stay warm and signal with a fire. In fact, if I'm just sitting still in the woods waiting to be found I can't think of much I NEED a kife for, nothing that would be more likely than hypothermia to kill me anyway.