In computer programming the improbability factor is a situation where a problem exists in a system. Frequently, the programmers are aware of the problem, but they are not allowed to fix the problem, solely because the chances of the problem ever surfacing are supposedly negligible compared to other problems that could be solved with the programmers' time and money. As a result, the problem may still occur and do heavy damage due to Murphy's law.
The improbability factor is an example of an anti-pattern.
References
Improbability factor Wikipedia(Text) CC BY-SA