It's hard to fit into a world where the average person really is dumber than you.
Quite the opposite, the 50% of the population has no problem to "fit into a world where the average person really is dumber than you."
The problem is not the intelligence of the kid, but the fact he thinks he's gifted. If you achieve good grades in school without effort and your parents constantly tell you you're gifted, you never really learn the correlation between effort and achievement. Then, suddenly, the real world kicks in. Other young adults, not gifted but learning none the less, catched up. Now they get the interesting jobs.
If you have contact to a gifted child, it's important to give him/her appropriate input. Put the focus on productive output, on effort (e.g. for a kid with math skills: Present interesting engineering problems, perhaps a bridge has to be built over a creek or something similar). On helping others and on developing the ability to communicate effectively with non-gifted kids (or adults).