They were exact opposites, if you thought about it.
House was gruff, bitter, unfriendly, antisocial, and carried an all around ragged appearance. Wilson was kind, considerate, always well-groomed, and the perfect go-to-guy for any problem.
House was surrounded by a seemingly un-penetrable shell, never letting anybody too close, while Wilson was like a human emotion magnet.
House viewed the world in shades of grey, and Wilson saw things through brilliant rainbow colored lenses.
One was perceptive and sharp, the other warm and inviting. And yet they still managed to stand each other, through any obstacles, in any situation. It was like a wolf and a deer wandering side by side through the dark forest, polar opposites, defying the fundamental laws of nature.
Wilson was the only one House trusted enough to let in, and Wilson knew him well enough to understand. No matter how bad things got, they would always help each other up. Because that was one quality they did share.
Loyalty.