In carrying out decision-making on risk then: (1) there may be possible sequences of future events which are not known about; or (2) there may be possible sequences which are known about but which are effectively ignored for one reason or another. Further, assumptions may be made which are not realistic; in relation to what has been considered. These issues are discussed and suggestions put forward in an effort to try to mitigate the effects of the implicit problems. Overall, it is desirable to be as open, explicit and cautious as possible in decision-making on risk in an attempt to allow for the un-anticipated. © 2004 Taylor and Francis Ltd.