They assign the electron (and other quantum particles) a wave-particle duality because sometimes it is in its wave-form (when we are not looking) and sometimes it is particle form (when we are looking).
But, take note, everything has a wave-particle duality – not just quantum particles.
Even the screen you are looking at has a wave-particle duality. It just so happens that things that are macro (i.e. things that we can see) exist in particle form simply because we can see them all the time. The probability wave still exists it is just so close to “1” most of the time that the macro item stays put. In theory, however, the screen could just pop out of existence.
To me, this begs a lot of questions.
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