It's easy transiting from C++ to Java/C#, the the reverse transition is not as easy. I would say that the "mental toolbox" of a C++ programmer includes a lot of things that also belong in a Java programmer's "toolbox" (i.e. classes, inheritance, virtual functions), which helps someone who knows C++ pick up Java relatively easily. But there are important aspects of C++ that are NOT in the Java toolbox, i.e. manual memory management, pointers, templates (which are way different from generics in java, by the way), these make the reverse transition harder.