There are two seemingly-contradictory entities at the heart of the quantum realm: quantum waves and particles, i.e., the fundamental wave-particle duality. Many aspects of the confusion and paradox in quantum physics are tied up with this duality. For example, the standard Copenhagen interpretation adopts an epistemic approach to the quantum wave (i.e., the wave reflects the state of our knowledge, and is not actually a physically real thing), which makes it difficult to understand what is happening in the double-slit experiment: how does an epistemic wave cause real interference effects?
The pilot-wave framework instead embraces the simultaneous and interacting reality of both particles and waves, and thus provides a simple explanation for the double-slit experiment: the particle goes through one slit, while the wave flows through both slits, and gives rise to the observed interference effects.
See mechanisms for a more detailed discussion for why the pilot-wave ontology seems to be essential for providing a (mostly) sensible understanding of the quantum realm.