I thought it was specifically about words with long e sounds? So "Keith" would be an exception (but it's a name and those are always weird - though "weird" itself is a better example), but most of the stuff on the mug it never meant to apply to. And overall for long e sounds it applies far more often than not. Ultimately english spelling will always be a clusterfuck though.

And I sure wish people would stop spelling wiener as weiner. The city is called Wien ffs.