It's mostly the steep curve of learning the platform you're trying to emulate. Start here: http://emu-docs.org/ http://emu-docs.org/ and read everything you ca

It's mostly the steep curve of learning the platform you're trying to emulate. Start here: http://emu-docs.org/ http://emu-docs.org/ and read everything you can get your hands on. Begin with the CPU and start emulating that. Then just start adding hardware bit by bit. It makes a lot more sense as you get into it. For NES emulation, the community at nesdev.com is amazing for assistance if you get stumped.