The assumption is wrong, plain and simple. Nothing behaves like the classical concept of particle or wave. There are edge cases where this is the case, and th

The assumption is wrong, plain and simple. Nothing behaves like the classical concept of particle or wave. There are edge cases where this is the case, and this is the reason the classical theories were and are still successful. And then there are cases where this breaks down catastrophically, like the double slit experiment. Which are the very reason we had to look for new theories. In this case, it is Quantumelectrodynamics, which perfectly explains the double slit and everything else concerning electromagnetic force. It is the most precise theory in any scientific field, with theoretical predictions matching measurements to 13 significant digits. Feynman, Schwinger and Tomanago got the Nobel in 1965 for this.