Calling on English experts!
Predictable - UnPredictable
You are said to be "predictable," if you are a bore completely devoid of creativity and prone to repetitiveness. You bore people to tears.
Then again, you don't want to be known to be "unpredictable" either. That means you are unstable and even dangerous because of your frequent outbursts.
So either way it is a bad thing although for personal safety, most of us would choose to be around predictable people over unpredictable psychopaths. Bring a book to read.
Can you think of other pairs of words in which both carry negative connotations? It almost seems like these two words are unrelated to each other even though they are just one prefix apart.