Difficult

You may wonder why I pretended to be Charles Dickens when I commented on the possibility of implanting an idea to another person.

Alas, it is the fault of Christopher Nolan.

In short, to fix up an idea in someone's mind by one dream, however florid it is, is exceedingly difficult, if not impossible. Yes, a single traumatic experience in real life often affect our behaviour permanently - especially if it happens during our childhood. You can consider it as a scar of psychological.

But, not a dream in solo.

The difference would be particularly prominent when we consider the type of idea. In general, a negative effect - that is, not to do something; you can also call it a deterring effect - is often resulted after a major event. For example, some of us avoid getting too close with the others after being hurt by a close friend of ours.

In contrast, it is far more difficult to induce a positive effect, such as working to ruin the family business as described in Inception.