After reading the many posts on systems, I am reminded of a chat I had years ago with a friend about grammar and its rules while discussing how difficult it is to learn a new language.
We were taught "I before E except after C" When someone who is trying to learn how to spell and pronounce English asks "what about the words neighbor, weight and vein?" what do you say? So you think about it and answer "Let's now say the rule is I before E except after C or when pronounced like an A as in neighbor and weigh." Another student is puzzled by the words deity and society. You tell him those are also exceptions because deity has 3 syllables (de-i-ty) and society has 4 syllables (so-ci-e-ty) But wait!
You begin to say "well, it's not really a science" and you suddenly realize that the very word 'science' doesn't follow the rule either. After all, in this case, the I is after the C, so why isn't it spelled sceince? Of course it's because it's pronounced 'sigh-ence' but it's still an exception. But what about conscience and efficient?
So you now have a headache and pour yourself a cup of coffee which has 'caffeine' in it, and you think "Gee, that's weird." Do you conclude that this so-called rule is a neither a rule or a system? You begin to list all of all the exceptions and write down as many as eighty words. (okay, that sounds like the letter A) So many exceptions....
Assuming there aren't thousands of words with ei or ie that do not follow the "I before E" rule, one can argue that if the rule is followed most of the time, the word will be spelled correctly. So it really isn't like a jackpot game with millions of combinations or even a pick-5 game with 376K. However, if you always apply this "rule" and one day participate in a challenging spelling bee with very tough competition, you will probably lose.