How many kata should one study?

A topic that's been done to death, but here's a nice quote from Hironori Ohtsuka, founder of wado ryu. Yes, I'm having a wado day today! And why not?

"Some falsely believe that mastery and progress come by knowing as many kata as possible. In the older days, one knew only about two or three at the most. Even to use one kata properly and efficiently is not an easy task. One must remember that it is quality over quantity when practicing any kata." - Hironori Ohtsuka


A classic comment there: to use one kata properly and efficiently is not an easy task.