Some might argue that the effect of the additional combat operations on equipment in Afghanistan is likely to be gradual particularly with the phasing-in of troops over the course of the year making it particularly difficult to predict the need to replace war-worn equipment.
The behaviour of short span railway bridges is known to be particularly difficult to predict due to the complexity of the coupled train track bridge system, as well as for being particularly sensitive to resonant phenomena.
With stocks facing their worst declines in decades, this year may be particularly difficult to predict.
Even in April none of this would have been particularly outlandish to predict.
The chief executive, Michel Pebereau, said the outlook for the remainder of the year "appears particularly difficult to predict".
What is more, there is added uncertainty since seasonal factors make June numbers particularly hard to predict.
Regional impacts are particularly difficult to predict, though some work has been done to map the risks in different areas of the UK.
The political contest in Canada this time is particularly difficult to predict since the three big parties each have about 30% in popular support.
Home Retail's chief executive, John Walden, said the recent rise of the late November sales bonanza, which only arrived in the UK in earnest last year, made it particularly difficult to predict how this year would play out.
