Patents cost $195 to file.
$1,500,000 to defend against in court.
As a result, Patent Trolls collect inane, invalid patents and use them to file thousands of lawsuits against small business and large business alike, claiming infringement of "their" idea.
The patent office has approved countless ridiculous patents that are clearly non-sensical or based on obviously long-known ideas, making it easy for trolls to collect ridiculous patents and use them as their flimsy excuse to file outrageously expensive lawsuits.
Small businesses, when faced with the specter of over a MILLION DOLLARS in defense fees, almost always SETTLE with the Patent Troll, paying out thousands rather than going through the cost and stress of a trial.
See http://www.x-plane.com/x-world/lawsuit for my story.