con·vo·luted [ˈkɒnvəluːtɪd, ˌkɒnvəˈluːtɪd]
adjective convoluted (adjective) (especially of an argument, story, or sentence) extremely complex and difficult to follow
A new mini-series called "Bring on the Bad Guys," which focuses on Loki, Doctor Doom, Green Goblin, Abomination, Red Skull, Dormammu and Mephisto has finished. The thread unifying all of these stories is Mephisto, who tasks these villains with a job early in their criminal careers. I've only read the Green Goblin and Red Skull books, but in both instances, Mephisto ordered them to commit murder.
So, we have more details emerging regarding Norman's first steps as the Green Goblin. After Norman agreed to sell Harry's soul to Mephisto for success and power, the demon also told him that he'd need to murder an employee of Osborn Industries named Alan Aardman. Norman was hesitant, saying that Alan was a family man but Mephisto knew that he was actually excited for the murder, pointing out the newly created Goblin costume. The Goblin killed Alan with a knife given to him by Mephisto and afterward, Norman's luck improved.
The original background given to the Green Goblin personality was explained in Amazing Spider-Man (vol. 1) #40, where Norman was changed in a laboratory accident.
"Cycles and Circles" explained in Spectacular Spider-Man Annual #14 that as a child Norman had seen his father beat his mother after his business failed. Norman took it on himself to kill the family dog (one less mouth to feed) before becoming obsessed with money and power. Norman repeated the violence he suffered onto his own son.
In Untold Tales of Spider-Man, he became frustrated with his proxies failures against Spider-Man, making him become the Green Goblin to deal with him personally.
"Darkness Calling" in Amazing Spider-Man (vol. 2) #25 has Norman explaining his childhood to a drugged and kidnapped Peter. He explained how his father left him alone in the mansion without electricity during a storm and how Norman learned to trust the darkness over the light.
According to "The Last Stand" in Marvel Knights: Spider-Man (vol. 1) #9, corrupt politicians and businessmen didn't want superheroes snooping around their doings and created supervillains to distract them. Norman was one of those businessmen but took on superheroes himself, instead of with proxies.
"Bring on the Bad Guys" themes stem from events in Amazing Spider-Man (vol. 5) #72, where we learn that Norman sold Harry's soul to Mephisto for his own success. He had been a good, caring father to Harry and his decision pained him.
Last year, "Shadow of the Green Goblin" showed Norman's failed marriage to Emily Lyman and her estrangement from Harry. Norman's mind was shattered after being exposed to psychochemicals produced by the Proto-Goblin, making him hallucinate creatures whispering to him. No mention of a demonic bargain.
The goblin formula itself has been re-imagined several times, from increasing strength and intelligence (despite the side effect of insanity) to a healing factor, to aging children born to a parents exposed to the formula. Amazing Spider-Man (vol. 6) #30 showed that the formula doesn't make induce insanity, it just brings out their inner selves. Tell that to Phil Urich, who went from good natured dork to psychopath.
I love a good psychological backstory but there comes a point when details become conflicting and confusing if too many writers want to leave their mark on a popular character. Character development becomes even more muddled when a writer decides to add a new aspect out of nowhere that completely contradicts continuity. A character needs to move forward and not be loaded down by too much past baggage.