a Pandora's box

a Pandora's box

a process that once begun generates many complicated problems.
In Greek mythology, Pandora was the first mortal woman. One story recounts that she was created by Zeus and sent to earth with a box or jar of evils in revenge for the fact that Prometheus had disobediently given the gift of fire to the earth. She let all the evils out of the container to infect the earth; only hope remained to ease the lot of humankind. In another account, the box contained all the blessings of the gods which, with the exception of hope, escaped and were lost when the box was opened.
1997 Spectator Drummond's series…has opened a Pandora's box of complaints… about the tide of mediocrity engulfing the art.
See also: box