I don't think that's true. What's your example? As far as I know any operation on a classical computer can be emulated on a quantum computer in some short amount of time; constant time, maybe.
i think essentially it's translating from classical logic gates operations to these weird gate types they have on quantum computers. This atleast, i think, is what 'compilers' do which target quantum computers or simulations.
There's a few types, and I imagine most things can be translated between them.
I think the most things are possible between the two, either will just be faster / more optimized for certain things, so it's less ideal to pick one or the other depending on what you're doing.
