This comprehensive review has looked at highlighting this work's namesake, that is to say each of the successes and failures in the state of the art of internal conversion from first principles. By exploring a variety of different methods which can each calculate rates of internal conversion, beginning from the formalisms' inception, to more modern day fine-tuning and benchmarking works, we have highlighted that while no robust model exists, many are quite successful and can be employed on most systems. Each has their own strengths and weaknesses, as well as degree of truncation, from complete to approximate.