The CAP theorem is a tool used to makes system designers aware of the trade-offs while designing networked shared-data systems. CAP has influenced the design of many distributed data systems. It made designers aware of a wide range of tradeoffs to consider while designing distributed data systems. Over the years, the CAP theorem has been a widely misunderstood tool used to categorize databases. There is much misinformation floating around about CAP. Most blog posts on CAP are historical and possibly incorrect.
It is important to understand CAP so that you can identify the misinformation around it.