Google paid $12.5B for Motorola Mobility — and sold it two years later for $2.9B

In 2012, Google acquired Motorola Mobility for $12.5 billion, the largest acquisition in Google's history at the time. The stated rationale was Motorola's patent portfolio — 17,000 patents that could defend Android against lawsuits from Apple and Microsoft. But Google also inherited Motorola's struggling phone business.

Under Google's ownership, Motorola continued to lose money. The phone business was not a strategic fit for a software and advertising company, and Google lacked the hardware expertise and distribution to turn it around. In January 2014, Google sold Motorola Mobility to Lenovo for $2.9 billion — a loss of $9.6 billion in under two years.

Google kept most of Motorola's patents, which was the original goal. But the $9.6 billion loss made the deal one of the most expensive patent purchases in history. The case illustrated the danger of acquiring a business for one asset (patents) and inheriting an entire operation (phone manufacturing) that you cannot run.