Also quantum fluctuations are examples of random events. They happen spontaneously: Out of the vacuum arises a pair of particle and antiparticle, which both live for a short time period and then annihilate again. Vacuum fluctuations are ubiquitous.

Vacuum fluctuations violate the often quoted philosophical principle 

> ex nihilo nihil = nothing comes from nothing.
 
From the viewpoint of quantum theory: Contrary to all apperances, according to Heisenberg’s uncertainty the corresponding violation of the principle of conservation of energy is admissible. Because for such pair of virtual particles the product of the indeterminacy of the lifetime ”Delta t” and the indeterminacy of the energy “Delta E” satisfies the uncertainty
 
Delta t x Delta E >= ½ ħ

Vacuum fluctuations play a fundamental role in Quantum Field Theory (QFT). Each field in QFT undergoes permanently quantum fluctuations.
 
For an introduction see https://en.wikipedia.org/wiki/Quantum_fluctuation, https://en.wikipedia.org/wiki/Vacuum_polarization

Phenomena like quantum fluctuations pose the question of validity of

> All that's not forbidden happens

as a principle for philosophy of nature.