Hot and cold are not opposites, but points on a scale. In reality, "cold" is much shorter than "hot"—absolute zero is a mere 273 celsius below zero, while there is no upper limit to how hot something can be. To assume duality there is to assume mankind’s normality as a universal measure of middle.

Same thing with white and black, light or dark, they too are merely a gradient of how much light is available or reflected by a certain item. They’re not opposites, they don't balance anything.

And "outside" is really all one place. How is it an opposite that we take pieces of "outside," build walls around it and call it "inside?" It’s still the same place, it’s just the building that was added.

There are a few dualities: magnetic poles, electric charge, direction, spin.