Let me begin by clarifying the term 'forced' - in this context I would describe it as any idea that was artificially realized against a criteria, rather than an idea that naturally evolved as a need to solve a problem. For example;
Forced: There is a lot of growth in X market, lets think of something new within that area
Natural: Booking taxis is such a pain, wouldn't it be nice for them to see my GPS coordinates - Uber is conceptualized.
That being said, how many of you have successfully built a startup based on an idea that was retrofitted to a set of criteria's (eg. Paul Graham's startups we'd like to fund essay) rather than as a solution to any of your problems.
Is a natural idea more likely to succeed than an artificial one?
As for what historically has been more successful, I don't know of any real metric that defines it. But I'd say from perception I have formed over the years, Natural ideas seem to win in terms of companies with a long term positive outcome.