The phrase "unstable equilibrium" refers to a situation where a system is delicately balanced but any slight disturbance will cause it to become unbalanced and potentially fall apart. Full definition
Many of the people returned a half century later, and the nation remained in unstable equilibrium until the conquest of Palestine by Alexander the Great in 332 B.C. Persecution under the overlord Antiochus Epiphanes, which forms the framework of the Book of Daniel with its lions» den and fiery furnace, led to the outbreak of the Maccabean rebellion. (religion-online.org)
The Gömböc is the first known homogeneous object with one stable and one unstable equilibrium point — leading it to move and «self - right» spontaneously without being touched. (geekwrapped.com)
It occurred to me that a superheated liquid, like a supersaturated vapor, might provide the desired unstable equilibrium that could be triggered by a small stimulus to yield a large effect. (scientificamerican.com)