B is correct. The Swiss cheese model describes the layering of multiple controls, in which control weaknesses in each layer appear like holes in a slice of Swiss cheese and act like their position constantly changes. In this model, all the control layers would have to fail simultaneously (i.e. the holes in all layers would need to be aligned) in order for an operational loss to result.

A is incorrect. The multiple control layers in a Swiss cheese framework imply that a failure of one control does not automatically result in a loss, since other control layers would need to fail too.

C is incorrect. In a Swiss cheese model, controls are structured so that the probability of failure of different controls are independent. While a decreasing probability of subsequent control failures would be beneficial, in practice, achieving this might not be realistic.

D is incorrect. In a Swiss cheese model, controls are assumed to be independent, and given this structure in which multiple controls must fail for an operational loss to occur, the probability of both smaller and larger losses is likely to decrease after the model is implemented.