Hello, I am fairly new to quantum physics, I am trying to understand where discrete quanta come from... I think that energy levels and particle angular momenta (and momentum?) are all quantised in quantum theory. Is there a simple explanation of why there must be discrete levels... is it some sort of unavoidable property of classical physics that it must be quantised at small scales... or is quantum theory just matching observed data at small scales? I'm looking for a sort of intuitive and simple explanation of the core reason why there must be quanta and not a continuum. Thanks for any help.