Since it opened up five years ago, TaskRabbit has often been a godsend to people with more money than time. The company stocks its auction house of personal assistants with people ready to deliver cupcakes to your office, or assemble your Ikea furniture, or clean your home. But last summer, executives at TaskRabbit noticed a problem. The percentage of completed tasks posted to the service's auction house had leveled off and was beginning to decline. Individual tasks were seeing fewer bids, indicating frustration on the part of the workers who used the site. The company was stumped: TaskRabbit added 1.25 million users to its system in 2013 and doubled its force of contractors to 25,000. Supply and demand were as big as they had ever been, the company says, but something wasn’t working.