Incomparable adjectives

False: that is the most unbelievable rule I have ever heard.

Well, ok, then is the word "unforgettable" comparable?
How about "inevitable"?

Reader's Digest still carries a column called 'My Most Unforgettable Character'. I suppose that some situation or other may call choosing for 'least inevitable' ending-- the point is that many so-called nongradable adjectives are in fact used in a graded fashion. Just look at the effort that is made to keep speakers from grading the most obviously non-gradables like 'unique' and 'alive'.

Thanks.

Just a quick followup: perfect?

From the United States Constitution:

We the people of the United States, in order to form a more perfect union, establish justice, insure domestic tranquility, provide for the common defense...