In Life of Pi the restrictions can be liberating because although Pi has immaginary walls around him and is mentally restricted by these barriers, it is instinct and human nature that when people are born someplace and grow up there, that is their home, it has everything they need, and it is safe. The whole time Pi is in the boat he is thinking about his life and ways of surviving. He learns from his father that these animals are dangerous, but he also learns from the strories about the animals who didn't escape when their cage was open, and if they did thay came right back. They came back because it was home, after all the time they spent in the zoo, they weren't ready for the outside and the cages weren't restricted places anymore because they wanted to be there. Pi sees there is a trust bond between the owner or workers and the animals. The animal knows that if they escape they won't have a source of food or a home anymore and it would be disloyal to the owners or workers. It is a kind of give and take situation between them. After all Pi learns a lot from this experience and learns to survive in a boat with a 450 Bengal Tiger. The fact that Pi could go no where allowed him to see past doing and creating but opening his mind to thoughts, ideas and so much more.
So in the end i think that restriction is just a word for being free but in your own space.