Rainsford's interactions with Whitney, the captain of the yacht, are very limited in Richard Connell's "The Most Dangerous Game" because Rainsford falls overboard shortly after their only conversation. We do know that they talk about two things: Ship-Trap Island and hunting. These are the two areas in which Rainsford is the realist and he believes Whitney is not.
First, Whitney thinks that animals experience fear of pain and fear of death. Rainsford, an expert big-game hunter, does not agree; more accurately, he does not even think about such things. He calls Whitney a philosopher and maintains the strong position that Whitney is "soft." Rainsford says:
"Be a realist. The world is made up of two classes--the hunters and the huntees. Luckily, you and I are hunters."
The other thing Rainsford thinks Whitney is not being a realist about is his view of the mysterious island known as Ship-Trap Island. Whitney buys into the superstitious beliefs of the sailors who all believe there is something ominous about the island. Whitney says,
"[S]ometimes I think sailors have an extra sense that tells them when they are in danger. Sometimes I think evil is a tangible thing--with wave lengths, just as sound and light have. An evil place can, so to speak, broadcast vibrations of evil. Anyhow, I'm glad we're getting out of this zone."
Rainsford is unmoved and unshaken by the sailors' beliefs or Whitney's feelings, and says these things are nothing but "[p]ure imagination." It will not be long before Rainsford realizes that Whitney was perhaps more of a realist than he thought, but for now he labels the ship's captain as an impractical, superstitious philosopher.