Almost all public funders now have policies for research data sharing. The general expectation is that publicly-funded research data are public good and therefore should be shared with as few restrictions as possible. The ideas behind policies for data sharing are noble, and created with the view of helping move ideas and science forward. However, there are some unexpected effects of data sharing policies. During this talk we will give examples of difficulties brought about with new funders' policies for sharing research data. We will discuss the concerns about the effects Open Data policies might have on collaborations (both academic and industrial), the academic competitiveness of researchers who share their data, the cost of data sharing, and the issues with data accessibility. We will then discuss a case study when data sharing was successful, and we will finish with take-home messages about the conditions that need to be met in order for data sharing to be a story of success.