You can think of them as being polar opposites on a spectrum. Depending on which one you are, it has a big impact on how you should manage your career and plan your days. If you’re neither you might be an Executor.
An Initiator is someone who has a lot of ideas and can begin new projects easily. An Initiator needs a team — badly. A Refiner is someone who maybe doesn’t have too many original ideas, but can improve on someone else's ideas, like an editor or an investor. An Executor might be a good CE