The Red Queen theory tells us that evolution is a harsh mistress. I've imagined mythologizing that, the embodiment of the evolutionary arms race as a blood-red Zerg Hydralisk hunter-killer, its red maw consuming the unfit, without mercy or conscience. Seems depressing, but might be a good idea too. The Dunning-Kruger effect says overconfidence is a systemic bias. Maybe an antagonistic memento mori would help us stay sharp and on our toes.
You could make up a whole pantheon of the demons of fail. Taleb's Black Swan dive-bombs down on the unsuspecting and complacent. Larry Niven already had "the dread god Finagle and his mad prophet Murphy."