In spite of his painful encounters with the world and its problems, Solomon does not recommend either pessimism or cynicism. Rather, he admonishes us to be realistic about life, accept God's gifts and enjoy them. He advises us to trust God and enjoy what we do have rather than complain about what we don't have.
The only people who really think they have seen something new are those whose experience is limited or whose vision can't penetrate beneath the surface of things. Because something is recent, they think it is new; they mistake now the for originality.