Is being 'predictable' a negative trait?

I am often told that I am very predictable. The ones who tell me this usually say it as if it is a negative trait. Multiple times I have been told to be more unpredictable and unexpected. On the rare occasion that I am unpredictable, people always say they like it. I never realized how obvious I am until I started college. My roommate is always telling me I’m too predictable.
If this is a negative trait, is there a way I can learn to become less predictable?
If it’s a positive trait, how can I help others to understand that?
Any opinion on the subject is welcome and appreciated.