You can be available, or you can be consistent. The higher guarantee of consistency you demand, lowers your availability.

Imagine a small database with a million copies on a million machines. when I write something, i'm going to have to wait a bit while all million machines acknowledge the write is complete. If i have a lower threshold, say 1, the write completes real fast but the million machines aren't consistent.

Real systems balance consistency and availability.

If I understand the author correctly: a CP system sacrifices Availability only during a Partition, whereas an AP system tends to sacrifice Consistency all the time.