noun
Murphy's Law
The adage that anything that can go wrong will go wrong. Often used humorously or resignedly when things don't go as planned.
マーフィーの法則で、大事な日に限って雨が降る。
By Murphy's Law, it rains only on important days.
またマーフィーの法則だよ。よりによって
It's Murphy's Law again. Of all times, the printer had to break now.