In Greek mythology Pandora was the first woman and Zeus presents her with a beautiful box but tells her she must never open it knowing that curiosity would eventually get the better of her. Pandora opens the box releasing evil into the world. In the bottom of the box was hope. This is basically the story of Eve in the Garden of Eden. In the Christian version God tells Eve she mustn't ever eat from the tree of knowledge but being the cunning little vixen she was she ate it anyway. Eating from the tree mankind lost its innocence and became like God in that they knew of good and evil. Eve and Pandora were both the first woman. Eve and Pandora disobeyed their god. Eve and Pandora brought evil to the world. This points to both Greek and Occidental mythology being rather misogynist. Women are beautiful but also the conduit for evil. They bring life but they also bring death.
But the serpent didn't lie or deceive. God told Adam and Eve that if they ate the forbidden fruit they would die that day which turns out to be deceptive. The serpent assured Eve that she would not die and that it would imbue her with God-like knowledge of good and evil which turned out to be true. In the Muslim version of the story it is Satan rather than the Serpent who entices Eve to eat the forbidden fruit and in that story Satan lies and tells Eve that the fruit would give her immortality.
Well it's Greek mythology and none of it is even close to being true. Pandora opened a box that held all the evil of the world and released it, and it seemed that there was no way to fix it. The only way to fix it was what stayed in the box which was hope. The saying "opening pandoras box" is just something that caught on over the years that we use to illustrate and describe a mess that seems hopless at the time.
Christians would say that the Serpent brought evil into the world. Smart Christians would say that it's also Jews and Muslims that use that story. Really smart Christians say the story, correctly interpreted (yours is not), is true but not historical.
It's something that makes a lot of complicated problems because something interfered with it.