It was Richard Parker who calmed down Pi. The irony of life is that the animal that scared him witless to start with was the same who brought him peace, purpose and even wholeness. They were literally and figuratively in the same boat. They had to live together. A part of Pi’s personality was glad about Parker’s presence, who gave him the will to hang on to life under the toughest conditions.
He realized danger and peace can co-exist when one is aware of one’s innate strength. He realizes the fact that staying with a tiger is less tormenting than living alone with despair. Loneliness and despair can easily kill a person. He decided to focus on the chances of survival and shut off the tragic circumstances he was placed in a lonely boat in the middle of Pacific Ocean.
In short, he became optimistic, balanced and stoical in his attitude to life thanks to the presence of Richard Parker.