relativity phenomenon is largely based on the duality principle
Not that I'm aware of. Which duality principle are you talking about?
http://en.wikipedia.org/wiki/Duality_(disambiguation)#Physics
the davisson and germer experiment proved the wave nature of electrons
Wave-particle duality perhaps? This is not particularly a relativity thing.
i wish to understand the cause of it
Why does it have to have a cause?
Wave-particle duality comes out of the way physics has historically been researched - the duality is in the physical models and not reality.
[We are like the three blind men investigating the elephant - "it's a rope" cries one, holding the tail; "no it's a wall", cries another, patting it's flanks; "nonono it's a snake" cries another wrapped in the trunk; the first two getting together may decide that an elephant has rope-wall duality - but actually it's an elephant.[*]]
In nature, an electron is an electron is an electron ... it is itself and not a wave or a particle. The wave and particle models are just a mistake we have realized we were making. So what causes mistakes?
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[*] in the corrollory - the wise man being investigated by three bind elephants - the elephants get a more consistent view of humans: all humans, they conclude, are flat.