|“||...It's not just about depth you know, you need the simplest version of the idea in order for it to grow naturally in a subject's mind; it's a very subtle art.||”|
Inception is the allegedly impossible task of implanting an idea in someone's mind via dream-sharing and making them think it is their own. However, as the movie progresses, it is proven that Inception is not impossible and has, in fact, been done successfully twice (both times by Dom Cobb). This method is believed to be the inverse of "Extraction".
Nonetheless, inception is a very difficult process. It requires dreamers to plant the idea in a dangerously deep layer of the Subject. This becomes the first difficulty of inception, as descending into a level so deep (three layers or more) creates highly unstable dream level. A way to solve the problem with unstable dreams is to use highly powerful sedatives, but such a powerful sedative makes escape by death in a dream impossible. Instead, death drops the dreamer in Limbo.
Another necessary component in inception is to have the Subject accept the idea with as little involvement from the dreamers as possible in presenting the idea to ensure the Subject cannot trace the origin of the idea. Part of this is to make the idea as simple as possible to ensure the idea remains.
Inception can be both incredibly useful, yet can also be incredibly dangerous. As Cobb said in the film "An idea can grow to either destroy or define you". In the case of the Fischer Job, the inception caused the downfall of a major energy company, stopping the company from becoming a new superpower. However, the inception that Cobb did on his wife, Mal, caused her death.
Inception is, of course, illegal due to the dangers that it poses, and also possibly moral issues that are not explored in the film. This makes it all the more important for the subject to not know the idea has been planted in their mind, as otherwise the dreamers could be traced and persecuted.