Isn't there similarly a big difference between "I don't know what will happen" and "anything could happen"?

Absolutely. This is a mistake that often occurs with people's understanding of how the (forward-looking) Many worlds hypothesis works.

entropy increases

One of these days, I have to take another crack at understanding entropy. The last time I attempted to wrap my head around it, all the definitions I could find seemed to have irreducible subjective elements. (Does any one reading this know of a good place to start?)