Sod's law

The phrase seems to derive, at least in part, from the colloquialism an "unlucky sod"; a term for someone who has had some bad (unlucky) experience, and is usually used as a sympathetic reference to the person.

A slightly different form of Sod's law states that "the degree of failure is in direct proportion to the effort expended and to the need for success."

An alternative expression, again in British culture, is "hope for the best, expect the worst".

Comparison with Murphy's law

Sod's law is a more extreme version of Murphy's law. While Murphy's law says that anything that can go wrong, will go wrong (eventually), Sod's law requires that it will always go wrong with the worst possible outcome or at the worst time. Belief in Sod's law can be viewed as a combination of the law of truly large numbers and the psychological effect of the law of selection. The former says we should expect things to go wrong now and then, and the latter says the exceptional events where something went wrong stand out in memory, but the great number of mundane events where nothing exceptional happened fall into obscurity. Sod’s law is also explained as a form of the natural human negativity bias, the survival trait of being extra alert to negative events.