What did Pi realize was wrong with his plan?

In Chapter 55, Pi realizes that he cannot outlast Richard Parker because fear and desperation will overcome everything else. He also realizes that he, himself, cannot survive on sea water.

A thought rang in my mind like an angry shout: "You fool and idiot! You dimwit! You brainless baboon! Plan Number Six is the worst plan of all! Richard Parker is afraid of the sea right now. It was nearly his grave. But crazed with thirst and hunger he will surmount his fear, and he will do whatever is necessary to appease his need. He will turn this moat into a bridge. He will swim as far as he has to, to catch the drifting raft and the food upon it. As for water, have you forgotten that tigers from the Sundarbans are known to drink saline water? Do you really think you can outlast his kidneys? I tell you, if you wage a war of attrition, you will lose it! You will die! IS THAT CLEAR?"