If the defendant committed the offense because of serious coercion, blackmail or duress, under circumstances not amounting to a complete defense, the court may depart downward. The extent of the decrease ordinarily should depend on the reasonableness of the defendant’s actions, on the proportionality of the defendant’s actions to the seriousness of coercion, blackmail, or duress involved, and on the extent to which the conduct would have been less harmful under the circumstances as the defendant believed them to be. Ordinarily coercion will be sufficiently serious to warrant departure only when it involves a threat of physical injury, substantial damage to property or similar injury resulting from the unlawful action of a third party or from a natural emergency. Notwithstanding this policy statement, personal financial difficulties and economic pressures upon a trade or business do not warrant a downward departure.