And in the Garbage In Garbage Out department:

We can talk about tracking  and big data and all those things, but at the end of the day the challenges are still accuracy, relevance, and – YES – privacy.

The data must be correct.
The data must serve an actual purpose
The data must be usable – that is, with the permission and concurrence of the owner.

Otherwise the data collection and storage system is broken.

Thanks to Thomas Redman and Harvard Business Review
How to Repair Your Data – Thomas C. Redman – Harvard Business Review