Some people always want someone else to do the dirty work. As with many things in life, this is also true with crime. Some people will try to get others to commit a crime rather than do it themselves.
Solicitation punishes anyone who deliberately encourages someone else to commit a crime. Though in most cases the solicitor will be the one who first thinks of committing a crime, he doesn't have to be. A person is also guilty of solicitation if he eggs on someone who has already decided to commit a crime.