See, Hollywood is convinced that sometimes there is just one specific thing that has to be discovered in order to cure a person of their shoelace-eating lunacy--or at least unravel the mystery behind it--long-term treatment and medication be damned.
Why It's Bullshit:
Simply put, psychology is not a game of Jenga, wherein one crucial block can bring down the entire tower of mental illness. No one factor made the person snap, and shoving one thing back into place won't make them whole. If it did, this mental illness stuff would be easy.
In the real world people with severe personality disorders are about as predictable as the weather, and so far the fact that we all know what causes lightning hasn't helped us figure out when and where it's going to strike with any kind of certainty.
For instance, think about all those cinematic serial killers brought to justice by the cunning insight of a psychological profiler. In real life that shit only leads to arrests about two percent of the time. The linked Malcolm Gladwell article took a comprehensive look at serial killer profiling and found that it's nothing more than cold reading - a parlor trick utilized by old-timey magicians and psychics to con people into thinking their mind was being read. People want to believe that Sherlock Holmes and his modern day incarnation, Dr. House (or Ben Matlock for you high-brow types) really exists. In reality, the only cases of successful psychological profiling were heavily doctored by the profilers themselves to make their predictions seem more accurate.
"And here's where I'll tell them the killer's address instead of screwing up everyone's lunch order like I actually did!"