The fundamental guideline for not deploying optimism is to ask what the cost of failure is in the particular situation. If the cost of failure is high, optimism is the wrong strategy. The pilot in the cockpit deciding whether to de-ice the plane one more time, the partygoer deciding whether to drive home after drinking, the frustrated spouse deciding whether to start an affair that, should it come to light, would break up the marriage should not use optimism.
