Without seeing more of the context, it's difficult to be sure what the author had in mind, but I would guess that he [or she] meant one of two things.
Either he meant that life would be very boring if the same things happened every day, and there were no surprises. So the best quality of life is experienced when one does not know what is going to happen in the immediate future.
Alternatively, on a more pessimistic note, the author may have considered that life was a series of major catastrophic changes which continually surprised and unsettled him. The best that one could hope for was that the future was merely unpredictable.
I would favour the first interpretation.