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Sam is the prototypical Knight of Cups. He has always seen himself as a prince in shining armour and is extremely idealistic (at least on the surface), to the point of appearing like Don Quixote at times.
In most portrayals, the Knight wears a cloak with fishes on it, which symbolizes consciousness and creativity. In contrast, Sam's cloak shows smiley faces, showing his love for popular culture, comedy, and pranks. The cloak's also yellow and pink, his two favorite colors.
The background is dry and barren, symbolizing the Knight of Cups' ability to turn that barrenness into something. Sam's doing just that with his movies, jokes, and advertising skills! He's got plenty of imagination to share with the world!