In a sense, most events are to a greater or lesser degree foreseeable. That does not mean that they cannot lead to frustration. Even events which are not merely foreseen but made the subject of express contractual provision may lead to frustration: as occurs when an event such as a strike, or a restraint of princes, lasts for so long as to go beyond the risk assumed under the contract and to render performance radically different from that contracted for. However … the less that an event, in its type and its impact, is foreseeable, the more likely it is to be a factor which, depending on other factors in the case, may lead on to frustration.