As an example, many people think that simply plugging a cool HDR image into a reflective material is a good realism technique, or using a neato HDR image as an Image Based Light.  These will almost certainly be very different from objects that are actually in the scene, and actually take away from realism rather than improve it.

Many people think cranking up a lot of Ambient Occlusion improves realism.  Again, it produces the opposite effect - it simply looks like a lot of AO and has little to do with how stuff behaves in reality since AO isn't especially based on how light is reflected.

People with hare lips and noses like Michael Jackson towards the end of his life are not a great element of realism either, nor are impossible proportions or fleshy masses that ignore gravity.

People standing on the tips of their toes while barefoot, or whose feet are levitating 1/2 inch off the ground, or who have something enclosed within their hands but clearly aren't actually touching it, or who have a crisp reflection of a room interior reflected in their eyes when they're apparently standing outdoors - I think you see what I mean.

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